مجله ایرانی علوم و تکنولوژی-الف
سال:1389 | دوره:34 | شماره:2-الف |تعداد مقالات:9

In this paper lightlike ruled surfaces in R31= ( R3, -dx2+dy2+dz2) are studied with respect to whether ruling curves are spacelike or null. It is seen that, in the first case the Gaussian curvature of the ruled surfaces vanishes. In the second case the Gaussian curvature of the ruled surfaces are negative. In the second case lightlike ruled surfaces are totally umbilical. Furthermore, lightlike surfaces of revolution are shown to be only cones, and the second type lightlike ruled surface.

In this paper, the Goursat problem of a third order equation on cases of explicit solvability is investigated, with the help of the Riemann function. Some results and one theorem are given concerning the existence and uniqueness for the solution of the suggested problem.

Reduced differential transform method (RDTM) is applied to various wave equations. To assess the accuracy of the solutions, we compare the results with the exact solutions and variational iteration method. The results reveal that the RDTM is very effective, convenient and quite accurate to systems of nonlinear equations.

Exact solution for steady two-dimensional flow of an incompressible magma is obtained. The magmatic flow is studied by considering the magma as a second grade fluid. The governing partial differential equations are transformed to ordinary differential equations by symmetry transformations. Results are discussed through graphs to understand the rheology of the flowing magma.

The electronic structure, energy band structure and electronic density of SnO2 ceramic in cubic phase have been investigated using first principle full potential-linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). Local density approximation (LDA) and the generalized gradient approximation (GGA), which are based on exchange- correlation energy optimization were used. The band gap was 2.2 eV at Γ point in the Brillouin zone within our approach. Calculations of the band structure and electronic structure of SnO2 were in a good agreement with the previous experimental and theoretical results with different approximations. Moreover, electronic density map shows that the bonding between Sn and O atoms is ionic.