In the present paper we consider the case of a Dirac field in a finite time domain and coupled to an external field. We decompose the field and its Hamiltonian in terms of creation and annihilation operators and path ...In the present paper we consider the case of a Dirac field in a finite time domain and coupled to an external field. We decompose the field and its Hamiltonian in terms of creation and annihilation operators and path integrate it via Grassmannian variables techniques. In that way we obtain its finite time domain Green function. We use it in the perturbative study of the interaction of Dirac particles with classical electromagnetic waves.展开更多
This paper mainly explores the electromagnetic perturbations of black holes in Gauss-Bonnet gravity and calculates the quasinormal modes for the 5-dimensional, 6-dimensional, 7-dimensional, and 8-dimensional black hol...This paper mainly explores the electromagnetic perturbations of black holes in Gauss-Bonnet gravity and calculates the quasinormal modes for the 5-dimensional, 6-dimensional, 7-dimensional, and 8-dimensional black holes. When α increases from zero, the imaginary part of w will increase accordingly till it reaches a maximum value where it starts to decrease. When a reaches zero, the quasinormal modes will approach their Schwarzschild values. If the Gauss-Bonnet coupling parameter α is large enough, the quasinormal modes will be proportional to α and the oscillation frequency will become high consequently . When L is large enough, the minimum value of -Im ω will approach a value too. We calculate that value for different dimensions.展开更多
We investigate the electromagnetic perturbation around a black hole with quintessence-like matter and a deficit solid angle.The complex frequencies of the quasinormal modes of electromagnetic perturbation are evaluate...We investigate the electromagnetic perturbation around a black hole with quintessence-like matter and a deficit solid angle.The complex frequencies of the quasinormal modes of electromagnetic perturbation are evaluated by the third-order WKB approximation.The results show that the electromagnetic perturbation around the black hole damps more slowly owing to the presence of the quintessence-like.The phenomenon can be distinguished from the black hole only with a deficit angle.展开更多
Based on the power dissipating model of spherical sample in free convection gas medium and the expression of input power, the model of temperature calculation for electromagnetic levitation melting sample was establis...Based on the power dissipating model of spherical sample in free convection gas medium and the expression of input power, the model of temperature calculation for electromagnetic levitation melting sample was established. Considering the limitation of levitation force and levitation sample temperature,the principle of stability levitation zone computation was determined. A spherical sample （ThDy）Fe2 under the protection of argon gas was examined, and the effect of radius of levitation sample and perturbation on the stable levitation zone was investigated. The results show that longitudinal perturbation and transverse perturbation can shorten the length of stable levitation zone and the range of levitation sample radius. By increasing the sample radius and weakening the perturbation the electromagnetic levitation melting stability of sample can be improved.展开更多
Based on the impedance/admittance rough boundaries, the reflection coefficients and the scattering cross section with low grazing angle incidence are obtained for both VV and HH polarizations. The error of the classic...Based on the impedance/admittance rough boundaries, the reflection coefficients and the scattering cross section with low grazing angle incidence are obtained for both VV and HH polarizations. The error of the classical perturbation method at grazing angle is overcome for the vertical polarization at a rough Neumann boundary of infinite extent. The derivation of the formulae and the numerical results show that the backscattering cross section depends on the grazing angle to the fourth power for both Neumann and Dirichlet boundary conditions with low grazing angle incidence. Our results can reduce to that of the classical small perturbation method by neglecting the Neumann and Dirichlet boundary conditions.展开更多
文摘In the present paper we consider the case of a Dirac field in a finite time domain and coupled to an external field. We decompose the field and its Hamiltonian in terms of creation and annihilation operators and path integrate it via Grassmannian variables techniques. In that way we obtain its finite time domain Green function. We use it in the perturbative study of the interaction of Dirac particles with classical electromagnetic waves.
基金Acknowledgments Thank Ding-Fang Zeng for very useful discussions.
文摘This paper mainly explores the electromagnetic perturbations of black holes in Gauss-Bonnet gravity and calculates the quasinormal modes for the 5-dimensional, 6-dimensional, 7-dimensional, and 8-dimensional black holes. When α increases from zero, the imaginary part of w will increase accordingly till it reaches a maximum value where it starts to decrease. When a reaches zero, the quasinormal modes will approach their Schwarzschild values. If the Gauss-Bonnet coupling parameter α is large enough, the quasinormal modes will be proportional to α and the oscillation frequency will become high consequently . When L is large enough, the minimum value of -Im ω will approach a value too. We calculate that value for different dimensions.
基金Supported by the National Natural Science Foundation of China under Grant No. 11147104
文摘We investigate the electromagnetic perturbation around a black hole with quintessence-like matter and a deficit solid angle.The complex frequencies of the quasinormal modes of electromagnetic perturbation are evaluated by the third-order WKB approximation.The results show that the electromagnetic perturbation around the black hole damps more slowly owing to the presence of the quintessence-like.The phenomenon can be distinguished from the black hole only with a deficit angle.
文摘Based on the power dissipating model of spherical sample in free convection gas medium and the expression of input power, the model of temperature calculation for electromagnetic levitation melting sample was established. Considering the limitation of levitation force and levitation sample temperature,the principle of stability levitation zone computation was determined. A spherical sample （ThDy）Fe2 under the protection of argon gas was examined, and the effect of radius of levitation sample and perturbation on the stable levitation zone was investigated. The results show that longitudinal perturbation and transverse perturbation can shorten the length of stable levitation zone and the range of levitation sample radius. By increasing the sample radius and weakening the perturbation the electromagnetic levitation melting stability of sample can be improved.
文摘Based on the impedance/admittance rough boundaries, the reflection coefficients and the scattering cross section with low grazing angle incidence are obtained for both VV and HH polarizations. The error of the classical perturbation method at grazing angle is overcome for the vertical polarization at a rough Neumann boundary of infinite extent. The derivation of the formulae and the numerical results show that the backscattering cross section depends on the grazing angle to the fourth power for both Neumann and Dirichlet boundary conditions with low grazing angle incidence. Our results can reduce to that of the classical small perturbation method by neglecting the Neumann and Dirichlet boundary conditions.
