Irregular phase-space orbits of the electrons are harmful to the electron-beam transport quality and hence deteriorate the performance of a free-electron laser （FEL）. In previous literature, it was demonstrated that...Irregular phase-space orbits of the electrons are harmful to the electron-beam transport quality and hence deteriorate the performance of a free-electron laser （FEL）. In previous literature, it was demonstrated that the irregularity of the electron phase-space orbits could be caused in several ways, such as varying the wiggler amplitude and inducing sidebands. Based on a Hamiltonian model with a set of self-consistent differential equations, it is shown in this paper that the electron- beam normalized plasma frequency functions not only couple the electron motion with the FEL wave, which results in the evolution of the FEL wave field and a possible power saturation at a large beam current, but also cause the irregularity of the electron phase-space orbits when the normalized plasma frequency has a sufficiently large value, even if the initial energy of the electron is equal to the synchronous energy or the FEL wave does not reach power saturation.展开更多
With the rapid urbanization process,ground collapses caused by anthropogenic activities occur frequently.Accurate susceptibility mapping is of great significance for disaster prevention and control.In this study,1198 ...With the rapid urbanization process,ground collapses caused by anthropogenic activities occur frequently.Accurate susceptibility mapping is of great significance for disaster prevention and control.In this study,1198 ground collapse cases in Shenzhen from 2017 to 2020 were collected.Eight effective factors(elevation,relief,clay proportion,average annual precipitation,distance from water,land use type,building density,and road density)were selected to construct the evaluation index system.Ground collapse susceptibility was analyzed and mapped using the normalized frequency ratio(NFR),logistic regression(LR),and NFR-LR coupling models.Finally,the result rationality and performance of the three models were compared through frequency ratio(FR)and ROC curve.The results indicate that all three models can effectively evaluate the ground collapse susceptibility(AUC>0.7),and the NFR-LR model result is more rational and has the best performance(AUC=0.791).The very high and high susceptibility zones cover a total area of 545.68 km^(2) and involve Nanshan,Luohu,and Futian District,as well as some areas of Baoan,Guangming,and Longgang District.The ground collapses in Shenzhen mainly occurred in the built-up areas,and the greater intensity of anthropogenic activities,the more susceptible to the disaster.展开更多
The dispersion properties in the short wavelength region of total internal reflective photonic crystal fiber have been studied by using the models of the equivalent twin waveguide soliton coupling,effective refractive...The dispersion properties in the short wavelength region of total internal reflective photonic crystal fiber have been studied by using the models of the equivalent twin waveguide soliton coupling,effective refractive index,effective normalized frequency and dispersion management solitons.It is shown that the dispersion in the cladding waveguide of the total internal reflective photonic crystal fiber is a positive dispersion,and the dispersion of its core waveguide is a negative dispersion.The method of the compensated probing laser diffraction by the phase hole induced by the stationary pumping laser in the cladding waveguide enables the average dispersion value of the total internal reflective photonic crystal fiber to be close to zero and the zero dispersion point to shift to the short wavelength region.展开更多
This paper analyzes the characteristic of matching efficiency between the fundamental mode of two kinds of optical waveguides and its Gaussian approximate field.Then, it presents a new method where the mode-field half...This paper analyzes the characteristic of matching efficiency between the fundamental mode of two kinds of optical waveguides and its Gaussian approximate field.Then, it presents a new method where the mode-field half-width of Caussian approximation for the fundamental mode should be defined according to the maximal matching efficiency method. The relationship between the mode-field half-width of the Gaussian approximate field obtained from the maximal matching efficiency and normalized frequency is studied; furthermore, two formulas of mode-field half-widths as a function of normalized frequency are proposed.展开更多
Single soliton and compound solitons are described by coupled-mode equation. It is noted that three parameters, which are dimensionless group velocity, normalized frequency, and grating strength, influence formed soli...Single soliton and compound solitons are described by coupled-mode equation. It is noted that three parameters, which are dimensionless group velocity, normalized frequency, and grating strength, influence formed solitons by emulation. The novel designs of parallel and serial multi-grating are advanced, and the compound solitons formed from parallel multi-grating are linear superposition; the compound solitons formed from serial multi-grating are nonlinear superposition, and finally two general formulae are obtained. Furthermore, it is theoretically shown that the compound grating solitons are prominent and flexible signals in optical communication.展开更多
基金Project supported by the Science Foundation of Department of Education of Sichuan Province,China (Grant No.12233454)the Youth Foundation of Department of Education of Sichuan Province,China (Grant No.10ZB080)the Xihua University Foundation,China (Grant No.Z0913306)
文摘Irregular phase-space orbits of the electrons are harmful to the electron-beam transport quality and hence deteriorate the performance of a free-electron laser （FEL）. In previous literature, it was demonstrated that the irregularity of the electron phase-space orbits could be caused in several ways, such as varying the wiggler amplitude and inducing sidebands. Based on a Hamiltonian model with a set of self-consistent differential equations, it is shown in this paper that the electron- beam normalized plasma frequency functions not only couple the electron motion with the FEL wave, which results in the evolution of the FEL wave field and a possible power saturation at a large beam current, but also cause the irregularity of the electron phase-space orbits when the normalized plasma frequency has a sufficiently large value, even if the initial energy of the electron is equal to the synchronous energy or the FEL wave does not reach power saturation.
基金jointed supported by the National Natural Science Foundation of China(Nos.41920104007,41731284)。
文摘With the rapid urbanization process,ground collapses caused by anthropogenic activities occur frequently.Accurate susceptibility mapping is of great significance for disaster prevention and control.In this study,1198 ground collapse cases in Shenzhen from 2017 to 2020 were collected.Eight effective factors(elevation,relief,clay proportion,average annual precipitation,distance from water,land use type,building density,and road density)were selected to construct the evaluation index system.Ground collapse susceptibility was analyzed and mapped using the normalized frequency ratio(NFR),logistic regression(LR),and NFR-LR coupling models.Finally,the result rationality and performance of the three models were compared through frequency ratio(FR)and ROC curve.The results indicate that all three models can effectively evaluate the ground collapse susceptibility(AUC>0.7),and the NFR-LR model result is more rational and has the best performance(AUC=0.791).The very high and high susceptibility zones cover a total area of 545.68 km^(2) and involve Nanshan,Luohu,and Futian District,as well as some areas of Baoan,Guangming,and Longgang District.The ground collapses in Shenzhen mainly occurred in the built-up areas,and the greater intensity of anthropogenic activities,the more susceptible to the disaster.
文摘The dispersion properties in the short wavelength region of total internal reflective photonic crystal fiber have been studied by using the models of the equivalent twin waveguide soliton coupling,effective refractive index,effective normalized frequency and dispersion management solitons.It is shown that the dispersion in the cladding waveguide of the total internal reflective photonic crystal fiber is a positive dispersion,and the dispersion of its core waveguide is a negative dispersion.The method of the compensated probing laser diffraction by the phase hole induced by the stationary pumping laser in the cladding waveguide enables the average dispersion value of the total internal reflective photonic crystal fiber to be close to zero and the zero dispersion point to shift to the short wavelength region.
基金Project supported by Natural Science Foundation of the Department of Science & Technology of Fujian Province of China (GrantNo 2007F5040)
文摘This paper analyzes the characteristic of matching efficiency between the fundamental mode of two kinds of optical waveguides and its Gaussian approximate field.Then, it presents a new method where the mode-field half-width of Caussian approximation for the fundamental mode should be defined according to the maximal matching efficiency method. The relationship between the mode-field half-width of the Gaussian approximate field obtained from the maximal matching efficiency and normalized frequency is studied; furthermore, two formulas of mode-field half-widths as a function of normalized frequency are proposed.
基金the National Natural Science Foundation of China(Grant No.40571097)Doctorial Innovative Foundation
文摘Single soliton and compound solitons are described by coupled-mode equation. It is noted that three parameters, which are dimensionless group velocity, normalized frequency, and grating strength, influence formed solitons by emulation. The novel designs of parallel and serial multi-grating are advanced, and the compound solitons formed from parallel multi-grating are linear superposition; the compound solitons formed from serial multi-grating are nonlinear superposition, and finally two general formulae are obtained. Furthermore, it is theoretically shown that the compound grating solitons are prominent and flexible signals in optical communication.
