Distinguishing close chirp-rates of different linear frequency modulation （LFM） signals under concentrated and complicated signal environment was studied. Firstly, detection and parameter estimation of multi-compone...Distinguishing close chirp-rates of different linear frequency modulation （LFM） signals under concentrated and complicated signal environment was studied. Firstly, detection and parameter estimation of multi-component LFM signal were used by discrete fast fractional Fourier transform （FrFT）. Then the expression of chirp-rate resolution in fractional Fourier domain （FrFD） was deduced from discrete normalize time-frequency distribution, when multi-component LFM signal had only one center frequency. Furthermore, the detail influence of the sampling time, sampling frequency and chirp-rate upon the resolution was analyzed by partial differential equation. Simulation results and analysis indicate that increasing the sampling time can enhance the resolution, but the influence of the sampling frequency can he omitted. What＇s more, in multi-component LFM signal, the chirp-rate resolution of FrFT is no less than a minimal value, and it mainly dependent on the biggest value of chirp-rates, with which it has an approximately positive exponential relationship.展开更多
We investigate the stability properties of optical solitons in a chirped PT-symmetric lattice whose frequency changes in the transverse direction. Linear-stability analysis together with the direct propagation simulat...We investigate the stability properties of optical solitons in a chirped PT-symmetric lattice whose frequency changes in the transverse direction. Linear-stability analysis together with the direct propagation simulations demonstrates that the chirped lattice can improve the stability of optical solitons dramatically. The instability of fundamental solitons can be completely suppressed if the chirp rate exceeds a critical value. A broad stability area of dipole solitons appears if the lattice is appropriately chirped. Thus, we propose an effective way to suppress the instability of solitons in PT-symmetric potentials.展开更多
Herein, a feasible method is proposed to compensate the high-order effect during bunch length compression, thereby enhancing the peak current of a highrepetition-rate X-ray free-electron laser source. In the proposed ...Herein, a feasible method is proposed to compensate the high-order effect during bunch length compression, thereby enhancing the peak current of a highrepetition-rate X-ray free-electron laser source. In the proposed method, the corrugated structure is inserted downstream of the high-order harmonic cavities to function as a passive linearizer and enhance the longitudinal profile of the electron beam. Three-dimensional simulations are performed to analyze the evolution of the longitudinal phase space, and the results demonstrate that the profile of the electron beam is improved and the peak current can be easily optimized to over 2 kA with a bunch charge of 100 pC.展开更多
We investigate the ionization dynamics of atoms by chirped attosecond pulses using the strong field approximation method. The pulse parameters are carefully chosen in the regime where the strong field approximation me...We investigate the ionization dynamics of atoms by chirped attosecond pulses using the strong field approximation method. The pulse parameters are carefully chosen in the regime where the strong field approximation method is valid. We analyse the effects of the chirp of attosecond pulses on the energy distributions and the corresponding left-right asymmetry of the ionized electrons. For a single chirped attosecond pulse, the ionized electrons can be redistributed and the left-right asymmetry shows oscillations because of the introduction of the chirp. For time-delayed double attosecond pulses at different intensities with the weaker one chirped, exchanging the order of the two pulses shows a relative shift of the energy spectra, which can be explained by the different effective time delays of different frequency components because of the chirp.展开更多
We describe a computational method for simulating the time dependent quantum mechanical system inter-acting with external field. In this method the Schr?dinger equation is solved by expanding the wave function in the ...We describe a computational method for simulating the time dependent quantum mechanical system inter-acting with external field. In this method the Schr?dinger equation is solved by expanding the wave function in the basis set of unperturbed Hamiltonian. The expansion yields a set of coupled first order differential equation. For expansion coefficients, the coupled channel method is applied to a particle in a box interacting with external field in the form of chirped laser pulse. The pulse shape is taken as Gaussian. We study the ef-fect of different pulse parameters i.e. chirp rate, intensity, center frequency, box length and laser duration on the dynamics of the particle. Many interesting results are obtained and explained.展开更多
目的探讨不同刺激速率chirp声诱发的健听青年听性脑干反应(ABR)的基本特征。方法对30例(男/女=13/17)健听青年行纯音测听、声导抗测试和不同声刺激率(11.1次/s、19.3次/s、51.1次/s)的chirp ABR反应阈值和潜伏期测试,并对结果进行分析...目的探讨不同刺激速率chirp声诱发的健听青年听性脑干反应(ABR)的基本特征。方法对30例(男/女=13/17)健听青年行纯音测听、声导抗测试和不同声刺激率(11.1次/s、19.3次/s、51.1次/s)的chirp ABR反应阈值和潜伏期测试,并对结果进行分析比较。结果在80 d B n HL高强度刺激时,不同声刺激率下chirp ABR的波Ⅲ、Ⅴ引出率均为100%,波Ⅰ的引出率分别为76.7%、76.7%、53.3%;随着刺激率的升高,chirp ABR波Ⅲ潜伏期延长,波Ⅴ反应阈增大、潜伏期延长,且差异具有统计学意义(P<0.05)。结论随着刺激率的升高,chirp ABR波形分化变差、引出率降低,建议临床采用低或中刺激率的chirp声诱发ABR。展开更多
基金Sponsored by the National Natural Science Foundation of China (60232010 ,60572094)the National Science Foundation of China for Distin-guished Young Scholars (60625104)
文摘Distinguishing close chirp-rates of different linear frequency modulation （LFM） signals under concentrated and complicated signal environment was studied. Firstly, detection and parameter estimation of multi-component LFM signal were used by discrete fast fractional Fourier transform （FrFT）. Then the expression of chirp-rate resolution in fractional Fourier domain （FrFD） was deduced from discrete normalize time-frequency distribution, when multi-component LFM signal had only one center frequency. Furthermore, the detail influence of the sampling time, sampling frequency and chirp-rate upon the resolution was analyzed by partial differential equation. Simulation results and analysis indicate that increasing the sampling time can enhance the resolution, but the influence of the sampling frequency can he omitted. What＇s more, in multi-component LFM signal, the chirp-rate resolution of FrFT is no less than a minimal value, and it mainly dependent on the biggest value of chirp-rates, with which it has an approximately positive exponential relationship.
基金the National Natural Science Foundation of China(Grant No.11074221)the Program for Innovative Research Team,Zhejiang Normal University,Jinhua,Zhejiang Province,China
文摘We investigate the stability properties of optical solitons in a chirped PT-symmetric lattice whose frequency changes in the transverse direction. Linear-stability analysis together with the direct propagation simulations demonstrates that the chirped lattice can improve the stability of optical solitons dramatically. The instability of fundamental solitons can be completely suppressed if the chirp rate exceeds a critical value. A broad stability area of dipole solitons appears if the lattice is appropriately chirped. Thus, we propose an effective way to suppress the instability of solitons in PT-symmetric potentials.
基金supported by the National Natural Science Foundation of China(Nos.11675248 and 11775294)the Youth Innovation Promotion Association CAS(No.2018300)
文摘Herein, a feasible method is proposed to compensate the high-order effect during bunch length compression, thereby enhancing the peak current of a highrepetition-rate X-ray free-electron laser source. In the proposed method, the corrugated structure is inserted downstream of the high-order harmonic cavities to function as a passive linearizer and enhance the longitudinal profile of the electron beam. Three-dimensional simulations are performed to analyze the evolution of the longitudinal phase space, and the results demonstrate that the profile of the electron beam is improved and the peak current can be easily optimized to over 2 kA with a bunch charge of 100 pC.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10704003 and 10821062)the National Basic Research Program of China (Grant No 2006CB806007)
文摘We investigate the ionization dynamics of atoms by chirped attosecond pulses using the strong field approximation method. The pulse parameters are carefully chosen in the regime where the strong field approximation method is valid. We analyse the effects of the chirp of attosecond pulses on the energy distributions and the corresponding left-right asymmetry of the ionized electrons. For a single chirped attosecond pulse, the ionized electrons can be redistributed and the left-right asymmetry shows oscillations because of the introduction of the chirp. For time-delayed double attosecond pulses at different intensities with the weaker one chirped, exchanging the order of the two pulses shows a relative shift of the energy spectra, which can be explained by the different effective time delays of different frequency components because of the chirp.
文摘We describe a computational method for simulating the time dependent quantum mechanical system inter-acting with external field. In this method the Schr?dinger equation is solved by expanding the wave function in the basis set of unperturbed Hamiltonian. The expansion yields a set of coupled first order differential equation. For expansion coefficients, the coupled channel method is applied to a particle in a box interacting with external field in the form of chirped laser pulse. The pulse shape is taken as Gaussian. We study the ef-fect of different pulse parameters i.e. chirp rate, intensity, center frequency, box length and laser duration on the dynamics of the particle. Many interesting results are obtained and explained.
文摘目的探讨不同刺激速率chirp声诱发的健听青年听性脑干反应(ABR)的基本特征。方法对30例(男/女=13/17)健听青年行纯音测听、声导抗测试和不同声刺激率(11.1次/s、19.3次/s、51.1次/s)的chirp ABR反应阈值和潜伏期测试,并对结果进行分析比较。结果在80 d B n HL高强度刺激时,不同声刺激率下chirp ABR的波Ⅲ、Ⅴ引出率均为100%,波Ⅰ的引出率分别为76.7%、76.7%、53.3%;随着刺激率的升高,chirp ABR波Ⅲ潜伏期延长,波Ⅴ反应阈增大、潜伏期延长,且差异具有统计学意义(P<0.05)。结论随着刺激率的升高,chirp ABR波形分化变差、引出率降低,建议临床采用低或中刺激率的chirp声诱发ABR。
