We study thermodynamic stability, mechanical properties, and microscopic mechanisms of transition metal monoboride TMB (take TiB, VB and CrB in 3d series; ZrB, NbB and MoB in 4d series; HfB, TaB and WB in 5d series as examples) by first-principles calculations based on density functional theory and plane pseudopotential wave method. We found thermodynamic stability and hardness anomalies of transition metal monoborides. In particular, as valence electron concentration is 8 e·(f.u.)^-1, thermodynamic stability is the most stable and hardness is the highest. To reveal its mechanism, we calculated electronic structure of TMB. As valence electron concentration of TMB is at 8 e·(f.u.)^-1, covalent bonding of pd blocked effectively dislocation slipping between metal bilayers, prevented shear deformation, and resulted in high hardness. These discoveries may help new superhard material designs.

Collisions between electrons in an ion source are analyzed theoretically.Processing models for null collisions between electron and other particles and Coulomb collisions among electrons are analyzed.With different storage and call mechanism,two Monte Carlo collision(MCC) processing models are developed.Then,MCC numerical models are added to a particle simulation software CHIPIC.With ion source JAERI 10A,the models ale verified.

An eighth-order Runge-Kutta(R-K)recurrence formula is constructed for differential equations.The formula i8 used tu simulate formation and movement of polarons in a one-dimensional poly-phenylenevinylene(PPV)molecular chain.The PPV chain composed of N carbons is described by an extended tight binding model.For N=160.the equations are solved by eighth.order R.K method.Stable polaron configuration and moving picture are obtained.Under electric field E=1×10⁵V×cm^-1.a poiaron moved along PPV chain at a velocity of 0.263 5Å·fs^-1.It indicates that the eighth-order R-K formula is applicable to carrier movement in organic molecules.

In a homogeneous equilibrum cavity model with solution of transport equations of liquid mass fraction, source terms controlling the transformation between gas and liquid and a compression method for pressure-density coupling are introduced. The RANS equations in a k-ε model with modified low Re of gas-liquid mixture are solved. Cavitation flows around an underwater vehicle at extremely small cavity numbers (σ=0.2~0.01) are simulated successfully. Clear cavity shape and inner structure are obtained. The variation of cavity length and maximal cavity diameter with cavity numbers is simulated and relation between drag force coefficients of the vehicle and cavitation number is shown. The method shows good convergence and stability in simulation of natural cavity at extremely small cavitation numbers, and shows high accuracy in predication of cavity shapes.

A method for generating three-dimensional unstructured viscous grids automatically is presented. High-aspect-ratio and anisotropic tetrahedral grid cells are constructed in viscous dominated flow regions by advancing-layers method (ALM).When the height of viscous grids reaches the requirement,the conventional advancing-front method (AFM)will generate isotropic grids to fill the remained flow regions.By the control of stretched function and background information,the transition from grids generated by ALM to isotropic grids generated by AFM becomes smooth and gradual.The unstructured viscous grids of M6 wing and the simple flow results of corresponding Navier-Stokes solution based on the present grid are also provided.

It focuses on an approach to generating 2D unstructured grids for the solution of Euler equations.Unlike the generation of unstructured grids before with background grids,the background information needed in Avancing Front Method is obtained directly with the distance to the airfoil surface.In solving the Euler equations,the cell centered finite volume method is used for space discretization,and four step Runge Kutta method is adopted for time marching.Two kinds of boundary condition are presented and three kinds of boundary conditions are applied and analyzed.The calculated results are given and discussed.

Using symbolic capabilities of MATHEMATICA software,a package(VCE 1.0) is developed to use for variational cumulant expansion study in lattice models with neiboring interaction.Enumerating high order connected diagrams and analytical expansions of free energy and so on can be obtained by this package.This package can also be used to study some models of lattice gauge theory and statistical physics.