With analysis on internal carrier transport mechanism in silicon carbide(SiC),an improved analytical model for dc current voltage and small signal parameters of 4H-SiC metal-semiconductor field effect transistor(MESFET) is proposed considering carrier velocity saturation and charge controlling.Incomplete dopant ionization and parasitic drain-source resistances are considered simultaneously.The simulated maximum transconductance is 48 mS·mm^-1 at a gate voltage of 0 V.Simulations and physical measurements show good agreement.The model is simple in calculation and distinct in physical mechanism.It is suitable for design and research of SiC devices and circuits.

A finite volume element method is used in an air pollution model.Trial function space and test function space are chosen linear element function space and piecewise constant function space,respectively.Error estimates of L² and H¹ are given.Numerical results of the finite volume element method and the finite difference method are analyzed and compared.It shows that the finite volume element method is much better and effective.

With analysis of conduction band structure and isotropic relaxation time approximation, an analytical model for the electron Hall mobility and Hall scattering factor of n-type 6H-SiC is proposed. The impact of different scattering mechanisms on the low field electron transport in 6H-SiC is illustrated clearly. Three ellipsoidal and parabolic constant energy surfaces simplification are used. The calculated results are in good agreement with physical measurements.

The electron transport properties in 2H-,4H-,and 6H-Silicon Carbide are investigated numerically with an ensemble Monte Carlo technique.The acoustic phonon deformation potential scattering,polar optical phonon scattering,intervalley phonon deformation scattering,ionized impurity scattering and neutral impurity scattering are considered.The electron mobilities of 2H-,4H-,and 6H-SiC as a function of temperature at low electric field are obtained.The influence of the neutral impurity scattering on the transport property of 4H-SiC is discussed in detail.Finally,the static and transient variation of electron drift velocity in high electric fields are studied.The peak transient velocity in an electricfield of 1.0×10⁶ V·cm^-1 is 3.3×10⁷cm·s~(-1) for 4H-Sic and 3.0×10⁷ cm·s^-1 for 6H-Sic when the electric field is applied perpendicular to the c axis.The simulated results are in good agreement with recent experiments in a wide range of temperature and electric field.

Several interpolation methods and their applications are focused on on one and two dimension fields.There are six interpolation methods:Shannon,cubic spline,cubic convolution,linear,FFT and cubic spline wavelet interpolations.The last one is based on wavelet sampling without frequency bandlimits.Two one-dimensional signals,i.e.,Shannon interpolation basis function and single pulse,are interpolated by the six methods.It is indicated that the cubic spline is the best interpolation for the frequency-bounded signal(Shannon basis), while the cubic convolution interpolation is the most accurate one among them for the single pulse signal.;Numerical interpolations are carried out for three reanalysis data sets produced by NCEP,National Center for Environmnet Prediction of the United States.Numerical results show that the cubic spline wavelet interpolation is of the highest accuracy for the monthly rainfall field,where the cubic spline interpolation is the best one for the monthly geopotential height field and the sea surface pressure field.The linear and the cubic spline wavelet interpolations are combined to avoid the negative rainfall produced by almost all the interpolations except for the linear one.This method can raise the rainfall interpolation accuracy too.One problem left is that the wavelet interpolation could produce"quot;Gibbs phenomena" by the boundary although it is smaller and more localized than Shannon interpolation.This difficulty remains to solve.

A single pulse and peak signals are decomposed and reconstructed with four types of wavelet bases in different orders. Results demonstrate that the biorthogonal wavelet is of a best fitting to the signals, and the Coifman wavelet is at the last in the four bases. After truncating the expansion series of the wavelets and the Fourier transform, the reconstruction shows that the wavelet reconstruction got higher precision with less number of non-zero coefficients and the local error distribution compared with the Fast Fourier transform we calculated. Thus the wavelet reconstruction can greatly attenuate "Gibbs phenomenon" and limit the errors in a narrow domain around the singularities of the signals.Besides, we also make expansions for the topography of Tibetan plateau in wavelets and Fourier transform. Its reconstruction with or without truncation shows the similar features as the one-dimensional signal reconstruction above.

A new algorithm to generate unstructured 3D surface grid is suggested,which can be generated directly on an arbitrary curved surface.The phenomenon similar to the triangular grid distortion produced by the mapping method is disappeared.The quality of the surface grid can be further improved by using Laplacian smoothing method easily.The algorithm can be used to provide highly qualified initial front for 3D unstructured grid generation.Several examples are presented.

The AUSM⁺ scheme which was developed on structured grid has been extended to be used on unstructured grid. The monotone linear reconstruction procedure using Green-Gauss theory is utilized to obtain second order spatial accuracy. Barth's limiter is employed to prevent solution spurious oscillations. An adaptive multigrid strategy is used to accelerate the convergence. Numerical results for several test cases are presented.

The Monte-Carlo method is applied to calculate the stray light of an infrared optical system.The system's geometrics tructure and the physical kinds of its elements are standardized.Some relevant probability models are established and a ray tracing approach is employed which can speed the calculation effectively.On the basis of those,an universal computer program is developed,and the stray light of an infrared camera has been analyzed.