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Electron correlation in triple differential cross sections for ionization of atomic hydrogen by electron impact is analysed for the case of coplanar asymmetric geometry within the framework of the two-potential formulae. Based on the approximations of projectile and faster-electron plane wave, the transition matrix element is analytically expressed to be a product of two factors: the correlation factor of two electrons in the final channel and the structure-scattering factor. The contribution of both the factors to the angular distribution of the triple differential cross section is calculated. The present results are compared with the experimental data and the other theoretical calculations for the incident energy of 150eV.

A novel model is proposed to study the ionization of atomic hydrogen by fast election impact in coplanar asymmetric geometry making use of the post form of the transition matrix element for the energy shell and the two-potential formula. Based on the approximation of projectile plane waves and three-body problems, the transition matrix element is decomposed into two parts: the structure and scattering factor and the correlation factor. The contributions of these factors to triple differential cross sections are investigated using the method of asymptotic and convergent series.

An analytic expression for the ionization amplitude of hydrogen by electron impact is found to contain a polynomial by an optimal truncation in an asymptotic series and a convergent series. The ionization amplitude, i.e., the transition matrix element on the energy shell, is decomposed into two parts: the structure-scattering factor and correlation factor, based on an approximation of the projectile plane wave in coplanar asymmetric geometries. The contribution of these factors to the triple differential cross section is evaluated using the method of optional truncation of asymptotic and convergent series.

According to the analysis of gain theory, the absorption or gain of medium depends on pump power. The coherent population oscillation leads the pulse to experience absorption saturation and propagation delay in a medium with absorption. This effect induces the pulse to experience gain saturation and propagation advance in a medium with gain. Making use of the transition rate equation of metastable state poplation, we develop the model of fast light in erbium-doped optical fiber and obtain the analytic expression of time advance. We demonstrate that there is a saturation effect of fast light in low frequency region, but the fast light is enhanced with pump power increasing in high frequency region.

Because of the absorption of erbium-doped optical fiber, the group velocity of the optical pulse propagation is slowed down and the intensity of signal is reduced, which brings more difficulties to the actual measurement of slow light and its application in communications, such as the distortion and the low measurement.Therefore only after the group velocity slowdown of light pulse in erbium-doped optical fiber under no absorption loss is realized, can the slow light technology really have the practical application. We investigate the erbium-doped optical fiber amplifier deeply and develop a technology, in which the different pump powers and fiber lengths are used to reduce the signal loss through theoretical calculation and realize the group velocity slowdown of light pulse. The results show that no absorption loss is realized at a pump power of 3.5 mW, and we realize the slow light with a fiber length of 0.1 m when the pump power is zero.

A classical trajectory Monte Carlo method is used to investigate the collision ionization of H by He2+ in Debye plasma, and the total and differential cross sections are obtained for collision energies of 5—400 keV/u in a large plasma parameter range. The interaction between charged particles is described by the Debye-Hückel model. Plasma screening changes the ionization energy and classical microcanonical distribution of bound electrons and the interaction between electron and the projectile, which result in the modification of ionization cross sections. It is found that both the total and differential cross sections increase with the increasing of screening interaction, and especially for energies below 10 keV/u, the cross sections are one to two magnitudes larger than those in the unscreened case. The emitted electron moves to the higher energy range, and the binary-encounter ionization mechanism becomes more important and a new hump appears due to the screening effect. Our unscreened cross section is in a good agreement with the experimental measurement for collision energies beyond 70 keV/u.

The interatomic potential function for the Fe-Cr-V-Ni-Si-C system multi-component alloys was constructed by fitting to the data of this alloy system via quantum chemistry ab initio calculation , first-principlespseudopotentials calculation and least squares method. The stability of the austenite matrixs of Fe-Cr-V-Ni-Si-C system alloys was examined by the acquired interatomic potential functions. The effect of Ni element on the stability of the alloy matrix was studied. The results of calculation show that the stability of austenite matrix with nickel content in the range of 1.02—2.03wt% increases with the increase of nickel content. When the nickel content in the alloys increases to 2.88 wt%, the austenite matrix energy increases and the stability of the austenite matrix decreases accordingly. The austenite matrix energy of N5—N8 alloy is lower than the energy of its martensite phase. Therefore, the microstructure of N5—N8 alloy tends to be of austenite-type. Analysis by XRD indicates that the matrix of N5—N8 alloy is mainly the austenite phase, complemented by martensite. The calculation results agree with the results of XRD.