An effective method to calculate the electron impact excitation cross sections of helium from ground state to a final channel in the whole energy region

The electron impact excitation(EIE) cross sections of an atom/ion in the whole energy region are needed in many research fields, such as astrophysics studies, inertial confinement fusion researches and so on. In the present work, an effective method to calculate the EIE cross sections of an atom/ion in the whole energy region is presented. We use the EIE cross sections of helium as an illustration example. The optical forbidden 1^(1)S–n^(1)S(n = 2–4) and optical allowed 1^(1)S–n^(1)P(n = 2–4) excitation cross sections are calculated in the whole energy region using the scheme that combines the partial wave R-matrix method and the first Born approximation. The calculated cross sections are in good agreement with the available experimental measurements. Based on these accurate cross sections of our calculation, we find that the ratios between the accurate cross sections and Born cross sections are nearly the same for different excitation final states in the same channel. According to this interesting property, a universal correction function is proposed and given to calculate the accurate EIE cross sections with the same computational efforts of the widely used Born cross sections,which should be very useful in the related application fields. The datasets presented in this paper are openly available at https://www.doi.org/10.57760/sciencedb.j00113.00142.

Impact vibration behavior of railway vehicles:a state-of-the-art overview

Excessive vibrations of railway vehicles induced by dynamic impact loadings have a significant impact on train operating safety and stability;however,due to the complexity and diversity of railway lines and service environment,they are extremely difficult to eliminate.A comprehensive overview of recent studies on the impact vibration behavior of railway vehicles was given in this paper.First,the sources of impact excitations were categorized in terms of wheel-rail contact irregularity,aerodynamic loads,and longitudinal impulses by train traction/braking.Then the main research approaches of vehicle impact vibration were briefly introduced in theoretical,experimental,and simulation aspects.Also,the impact vibration response characteristics of railway vehicles were categorized and examined in detail to various impact excitation sources.Finally,some attempts of using the railway vehicle vibration to detect track defects and the possible mitigation measures were outlined.