Molecular dynamics simulation is used to simulate response of nonlinear sinusoidal alternation flow of helium gas oscillation in a pulse tube. Formation of axial pressure wave and temperature field inducted by gas oscillation was studied.Influence of length to diameter ratio on temperature difference and phase of cold and hot ends of the pulse tube is shown. It shows that the pressure wave,speed wave and mass flow wave accompanying by driving force are similar to a sinusoidal function while the temperature wave is similar to a half-sinusoidal function. The oscillation period is shortened with increase of the diameter of the tube and prolonged with increase of the length of the tube. The maximum temperature difference between hot end and cold end increases with the length of the tube but independent of diameter. It is predicted that there is an optimal aspect ratio and oscillation period for pulse tube with different diameter, which increases with increasing of the diameter. It provides a theoretical basis for optimizing efficiency of pulse tube.

Electronic properties of graphene nanoribbons (GNRs) doped with rhombus boron nitride segments are investigated by using first-principles method based on density functional theory. It is shown that band gaps of AGNRs increase owing to doping, and band gaps of AGNRs vary slightly as doped at different positions. In nonmagnetic states, ZGNRs are metal whether or not it is doped. In ferromagnetic states, ZGNRs change from metal to semiconductor due to doping. In antiferromagnetic states, ZGNRs are semiconductor whether or not it is doped, but band gaps are changed owing to doping. Structures of doped AGNRs and ZGNRs are stable, and ground state of doped ZGNRs is antiferromagnetic. It suggests that rhombus boron nitride segments doping controls effectively properties of GNRs, which is positive on future graphene nanoelectronic devices.

For energy deposition of fast electrons in high density plasma, a relativistic Fokker-Planck equation in three-dimensional momentum space is introduced. It includes both binary collision and contribution from plasma collective response. Numerical method as well as kinetic code of the equation is developed. Typical energy deposition cases are presented with comparison with stopping power model. Energy deposition of fast electrons with energy from 0.5 MeV to 3.5 MeV in 300 g·cm^-3 DT plasma are simulated. It shows that scattering angle ϕ plays minor role on range and penetration depth of energy deposition of fast electrons.

We study numerical method for relativistic Vlasov equation and present a scheme for computing Vlasov equation based on Cartesian-spherical coordinate system, which can be used to reduce number of numerical grid for momentum space. Furthermore, a 4th order non-splitting finite volume scheme is proposed in order to solve momentum parts of relativistic Vlasov equation. In test problems, especially relativistic Landau problem, laser-plasma interaction are solved by using the scheme. We confirm the scheme with theoretically analysis as well as numerical comparison with results of PIC method.

An improved time-delayed dual model for internet congestion control is investigated.Normal form theory,center manifold theorem and Hopf bifurcation theory are used for analysis.Bifurcation and stability analysis are mainly decided by communication time delay.As the delay passes through a critical value,Hopf bifurcation forms,which leads to a large oscillation of link price function.In addition,bifurcation direction and bifurcation periodic solution are derived,which provide model design with theoretical foundations.This work is summarized as two theorems verified by numerical simulations.

A fractal theory for double porous media reservoir is introduced. An effective well radius mathematical model is used to calculate pressure of non-stesdy flow in a complex intluent system considering wellbore storage, skin factor and phase redistribution. With Douglus-Jones predictor-correcter method we obtain numerical solution of infinitely large system with constant rate production. Entire drawdown curve of the complex influent system includes 4 periods. Effects of phase redistribution parameters, double porous media parameters and fractal parameters on drawdown are shown in typical pressure curves.

For boundary conditions with functions changing rapidly,especially in charged conductors,we combine compact feature of wavelet functions and high accuracy of RBF in a coupled method and solve ground metal trough/box problems. Rectangular,ridge and round waveguides are analyzed with RBF and FEM methods.Numerical experiments show that RBF method is efficient in solving electromagnetic boundary and eigenvalue problems.RBF method is easier and more accurate with less nodes.

An iterative physical optics(IPO) method combined with multilevel fast multipole algorithm(MLFMA) is used to solve electromagnetic scattering by a three-dimensional complex cavity efficiently and rapidly.The iterative formulations of hybrid algorithm are derived.For slow bending cavities in engineering,a proper subsection structured grouping method is provided to avoid the shelter of facets between two groups.A generalized reciprocity integral(GRI) method is applied to cavities with complex termination.The methods obtain accurate results and improve computing speed.

Based on the stream function-vorticity expression a discrete procedure is employed to approximate the imcompressible fluid with zero viscosity,in which the vorticity is approximated by finite difference along its streamline,the velocity field and the stream function are approximated simultaneously by a mixed finite element.The analysis shows that the procedure possesses both high accuracy and good stability which are not shared by standard methods.

A Monte Carlo simulation code has been written for heavy-ion induced fission at sub-barrier energies with a simple model. The final properties of the heavy fragmemts such as mass, charge, energy, angular distribution and angular correlation have been simulated for complete fusion-fission and transfer-fission. The angles and velocities of the fragments relative to the recoil direction are given in the laboratory system. Consideration covers the combined kinematic effects of the distributions in mass energy and angular for the heavy fragments and pre-scission, post-scission neutron emission. The code can be used as a tool for experiment planning and analysis.