A model for an open four-level atomic system driven by two fields is presented. Density matrix equations of motion are obtained by electric dipole and rotating wave approximations. Physical mechanism of lasing without inversion (LWI) is discussed. Effects of detuning on gain without inversion and population difference are studied. Dispersion equals to zero as two driving and probe fields are resonant. As one driving field (probe field) is resonant, the gain and the population difference versus detuning of driving field (probe field)show even symmetry, and the dispersion shows central symmetry. As two or three of driving and probe fields are off-resonance, the symmetries disappear. LWI gain is obtained when the dispersion equals to zero. When beth driving and probe fields are off-resonance, the gain, the dispersion and the population difference change greatly. High dispersion without absorption is obtained by adjusting suitable parameters of the system.

A model of the beam centroid motion in a linear induction accelerator(LIA) was developed. It calculates the track of the beam centroid under the condition of cell magnet misalignment. The 3D magnetic field distribution is calculated with a coordinate transform. The track of the beam centroid is given by a coupled solution of the beam centroid and envelope equations. Quantitative relation between the transverse displacement of beam centroid and the misalignment of magnets is useful in the installation of magnets and the adjustment of steering coils.

A calculation model of accelerator beam envelope has been developed. It can predict beam envelope in linear induction accelerator from the injector to the final focus region. Its code can easily calculate the effect of various electric and magnetic element parameters on the beam. As calculating examples, the envelopes of 3 kA-beam current under the condition of 40 m long magnetic profiles are given.

A numerical simulation method is presented for calculating two dimensional two-stage light-gas gun impacts to launch flier to hypervelocity.It uses the complex algorithm, concerned with the treatment of multi-materials, multi-interfaces, huge distortions and high density ratios etc. Basing on multi-fluid VOF and PPM methods, we develop the MFPPM2 shock wave physics code to simulate the Sandia hypervelocity impaction experimental confighuration model. Some results from the MFPPM2 are griven and appear to be in good agreement with those of the CTH code in Sandia Laboratory.

Level Set (LS) function for tracking multi-fluid interfaces and the different materials corresponding to different leves are applied.These LS equations together with fluid dynamic Euler equations are solved independently.An adaptive mesh refinement (AMR) method in the context of Cartesian grids is discussed at the same time.Such an approach can be automatically adaptive in that it chooses the regions of refinement based on the behavior of the solution while for time dependent problems the regions of refinement must change with time.There are two main strategies that have been used to handle the data structures involved when a rectangular grid is being refined.One approach is to refine individual grid cells as needed,typically by splitting a single cell in two dimensions into four pieces.Each of these pieces may be further subdivided recursively,depending on how many levels of refinement are allowed.High resolution results can be given by using this method,and it can also track the shock front adaptively and save CPU greatly.

Electron-impact excitation collision strength Ω(nl-n'l')(3≤n≤7,4≤n'≤7) among configuration-average levels for the Ni-like Ions Pb⁵⁴⁺, Au⁵¹⁺,Ba²⁸⁺,Mo¹⁴⁺,Ge⁴⁺ have been calcuated systematically using the quasirelativitic distorted-wave methods. In addition, the collision strength in high limit have been calculated. The data for the collision strength or thermally averaged rate coefficient over the whole range of energy or temperature have been evaluated by a least-squares spline fitting procedure. As a result, the collision strength with arbitrary electron energy and rate coefficient with arbitrary temperature can be determined by ten parameters.

The problem of the slow convergence has been resolved in partial wave expansion for the excitations of electron-ion collisions, with three approximations including plane wave, coulomb Bethe and equimultiple decrease series. As an example, we have computed some important transitions of Ne-like Ge ion and made comparisons between the results obtained by three approximations. The results slow-that all the three methods are acceptable.

In this paper a numerical simulation for intake water temperature and aquatic environment temperature field of cooling water system for the thermal power plant under the action of tide motion by using the hybrid method of fractional steps with L_∞-stability^[5] is given, and its hydro-thermal behavior and environment pollution are predicted. The computed elevation of water and velocity field are in good agreement with the prototype observations, and the average intake water temperature and aquatic environment temperature distribution are also in consistent very well with the laboratory experiments.