This paper presents the Mei symmetries and new types of non-Noether conserved quantities for a higher-order nonholonomic constraint mechanical system. On the basis of the form invariance of differential equations of motion for dynamical functions under general infinitesimal transformation, the determining equations, the constraint restriction equations and the additional restriction equations of Mei symmetries of the system are constructed. The criterions of Mei symmetries, weak Mei symmetries and strong Mei symmetries of the system are given. New types of conserved quantities, i.e. the Mei symmetrical conserved quantities, the weak Mei symmetrical conserved quantities and the strong Mei symmetrical conserved quantities of a higher-order nonholonomic system, are obtained. Then, a deduction of the first-order nonholonomic system is discussed. Finally, two examples are given to illustrate the application of the method and then the results.

https://iopscience.iop.org/article/10.1088/1674-1056/20/3/030202/pdf

Mei symmetries and Mei conserved quantities for higher-order nonholonomic constraint systems

We study the ultraslow optical solitons in a resonant three-level atomic system via electromagnetically induced transparency under a density-matrix (DM) approach. The results of linear and nonlinear optical properties are compared with those obtained by using an amplitude variable (AV) approach. It is found that the results for both approaches are the same in the linear regime if the corresponding relations between the population-coherence decay rates in the DM approach and the energy-level decay rates in the AV approach are appropriately imposed. However, in the nonlinear regime there is a small difference for the self-phase modulation coefficient of the nonlinear Schrodinger equation that governs the time evolution of probe pulse envelope. All analytical predicts are checked by numerical simulations.

Ultraslow optical solitons via electromagnetically induced transparency: a density-matrix approach

A mechanism for producing hydrogen anions in a low density, low energy hydrogen plasma is proposed. The observation in a plasma ion source that the anion output is quadratically related to the Lyman-α radiation suggests that anions could be formed in collisions between atoms in the first excited state. A potential energy plot for the hydrogen molecule is developed that includes a high energy ionic state, comprising a proton and the weakly bound H−(2p2 3Pe) ion, revealing a path to stable anion formation.

H− formation by neutral resonant ionization of H(n=2) atoms

We numerically simulate three-photon absorption spectra in a three-coupled-quantum-well nanostructure interacting with a pump field, a coherent coupling field, and a probe field. We find that the three-photon absorption spectra can be dramatically influenced due to the intensities of the coupling field and pump field changing under the three-photon resonance condition. The effect of the frequency detuning of the pump field on the three-photon absorption spectra is also discussed. The study in our case is much more practical than the study in the case of its atomic counterpart in the sense of flexible design and the wide adjustable parameters. Thus it may open up some new possibilities for technological applications in optoelectronics and solid-state quantum information science.

https://iopscience.iop.org/article/10.1088/1674-1056/19/5/054205/pdf

Steady-state analysis of three-photon absorption spectra via density-matrix method in a three-coupled-quantum-well nanostructure

In the framework of the time-dependent local density approximation, applied to valence electrons, coupled non-adiabatically to molecular dynamics of ions, we investigate the microscopic mechanism of collisions between low energetic protons and ethylene. Not only the amount of energy lost by the projectile, but also the electronic and vibronic excitations of the target are identified. We find that the energy loss of the proton and excitation dynamics of the target depends sensitively on the impact energy.

Collision of Low Energy Proton with Ethylene

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-Huckel 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.

Plasma screening effect on the differential cross sections of collision ionization of H by He2

The He 2+ ＋H Impact Ionization process is investigated using a continu um distorted wave method with the eikonal initial-state(CDW-EIS) approximation.The total,single- and double-differential cross sections are obtained in the projectile energy ranges from 30keV/u to 2000keV/u.The total cross sections are compared with the existing theoretical and experimental data.When the projectile energy is larger than 100keV/u,our results are in good agreement with the experimental measurements,while about 50% less than experimental data in the lower energy range.The ionization mechanism of soft-collisions,electron captured to continuum states and binary-encounter collisions are also displayed.

CDW-EIS calculation in He 2+ +H impact ionization

Cross sections of electron-loss in H(ls)+ H(ls) collisions and total collisional destruction of H(2s) in H(ls) + H(2s) collisions are calculated by four-body classical-trajectory Monte Carlo (CTMC) method and compared with previous theoretical and experimental data over the energy range of 4–100 keV. For the former a good agreement is obtained within different four-body CTMC calculations, and for the incident energy Ep > 10keV, comparison with the experimental data shows a better agreement than the results calculated by the impact parameter approximation. For the latter, our theory predicts the correct experimental behaviour, and the discrepancies between our results and experimental ones are less than 30%. Based on the successive comparison with experiments, the cross sections for excitation to H(2p), single- and double-ionization and H- formation in H(2s)+H(2s) collisions are calculated in the energy range of 4–100keV for the first time, and compared with those in H(ls)+H(ls) and H(ls)+H(2s) collisions.

https://iopscience.iop.org/article/10.1088/0256-307X/25/8/032/pdf

Theoretical Investigation on Excitation, Ionization and Capture in H(1s,2s) +H(1s, 2s) Collisions

CTMC calculation of O3++He impact processes

CTMC calculation of Si2+ + H impact ionization

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