With first-principles density functional theory, geometric structures of pure LiMgN, Mn-doped LiMgN, and Mn-doped LiMgN with excess or deficient of Li are geometrically optimized. Electronic structures, magnetic properties, and optical properties were calculated. It shows that Mn doping produces spin polarized impurity bands, which makes materials exhibit half metallic properties. Their properties are affected by stoichiometry of Li. Deficient of Li makes width of impurity band, net magnetic moments and Curie temperature decrease, while half metallic increase. Excess of Li improves width of impurity band, conductivity and Curie temperature, which makes half metallic and band gap decrease. Mn-doped systems have a new dielectric peak in low-energy region, which enhances absorption of low-frequency electromagnetic waves, and shows red-shift. There is an obvious change in complex refractive index function. Energy loss decreases and blue-shift appears only in Li-deficient compound.

Nematic droplets are studied with Monte Carlo simulations with a modified Gruhn-Hess pair potential. The potential is spatially anisotropic and potential parameters are related to elastic constants K₁₁ ,K₂₂ ,K₃₃ and surface-like elastic constant K₁₃. It is assumed that nematic droplet surface is a free surface. Second order parameters and introrse intensity, which describes quantitatively intrinsic anchoring induced by surface at low temperatures, are calculated with a modified Gruhn-Hess pair potential and are compared with those in Gruhn-Hess model I. It is shown that the modified model with K₁₃ induces intrinsic anchoring near droplet surface, orientation and intrinsic anchoring strength depend strongly on K₁₃, and introrse intensity is related to K₃₃/K₁₁. Order degree of nematic droplet is lower from inner shell to outer shell due to incomplete anisotropic nematic-nematic interactions.

Left kink (LK) and right kink (RK) migration and velocity at different temperatures and shear stresses are obtained with molecular dynamics (MD) method. By means of nudged elastic band method (NEB) based on tight binding (TB) potential, migration energies of LK and RK are calculated. It shows that due to high migration energy a single LK or RK moves slowly. Multiple kink pair structure of LK and RK-reconstruction defect (RC) dissociated from RK accelerate motion of LK and RK. Particularly, RC makes 30° partial dislocation move faster.

It describes an improved numerical model and calculation method for stability simulation of a pulse tube refrigerator.A set of differential equations based on the conservation of mass,energy and momentum for oscillating fluid flow is solved by numerical method.A variety of physical factors,such as actual gas,gas flow friction,heat transfer in the heat exchanger and regenerator,ect.are included to improve the accuracy of the model.The results show the changes of mass flow,pressure,temperature,enthalpy flow and so on in each cell with time.The computer predicted performance is compared with the experimental data.Good agreement has been found between the two.