JOURNAL OF SCIENCE (KHARAZMI UNIVERSITY)
Year:2013 | Volume:13 | Issue:2|Papers Count:8

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In this research work nano porous silicon layers with different porosity were prepared by using electrochemical etching. Surface morphology and size of pores were investigated by scanning electron microscopy (SEM). TiO2 thin films with EBPVD method have been deposited on the surface of PSi layers. The influence of anodization conditions such as anodization time interval and current density on electrical properties and surface morphology of sandwich devices were carried out using I-V measurements .The results showed that, electrical properties were influenced by changes of current density and anodization time interval. We also investigated the AC electrical conductivity of Al/TiO2/PSi/Al sandwich devices over the range of frequency 102 to 105 Hz and temperature range 300 to 378 K. It is known that, over the range of frequency<103Hz the band theory and over the range of frequency>103Hz hopping mechanism is applicable in explaining the conductivity of TiO2/PSi thin films nano structures with aluminum electrodes.

In this article , efficient numerical methods for finding solution of linear and nonlinear Fredholm integral equations of the second kind based on Bernstein multi scaling functions are presented . Initially, the properties of these functions, which are a combination of blockpulse functions on [0,1) , and Bernstein polynomials with the dual operational matrix are presented. Then these properties are used for the purpose of conversion of the mentioned integral equation to a matrix equation which is compatible to an algebraic equations system. The imperative of the Bernstein multi scaling functions for proper quantitative values of m and k, have a high accuracy and specifically the relative errors of the numerical solutions will be minimum. The presented methods from the computational viewpoint are very simple and attractive and the numerical examples at the end show the efficiency and accuracy of these methods.

In this paper, we study the Arens regularity properties of module actions and we extend some proposition from Baker, Dales and Lau into general situations. We establish some relationships between topological centers of module actions and factorization properties of them with some results in group algebras.

Let (R, m) be a Noetherian local ring, a an ideal of R and M a finitely generated R-module. We investigate some properties of formal local cohomology modules with respect to a Serre subcategory. We provide a common language to indicate some properties of formal local cohomology modules.

In this paper, a collocation method based on the Bessel polynomials is used for the solution of nonlinear Fredholm-Volterra-Hammerstein integro-differential equations (FVHIDEs) under mixed conditions. This method of estimating the solution, transforms the nonlinear (FVHIDEs) to matrix equations with the help of Bessel polynomials of the first kind and collocation points. The matrix equations correspond to a system of nonlinear algebraic equations with the unknown Bessel coefficients. Present results and comparisons demonstrate that our estimate has good degree of accuracy and this method is more valid and useful than other methods.

Inverse time-dependent heat source problems have an important role in many branches of science and technology. The aim of this paper is to solve these classes of problems using a variational iteration method (VIM). The method applied does not require discretization of the region, as in the case of classical methods based on the finite difference method, the boundary element method or the other methods. Applying this method, we obtain a stable approximation to an unknown source term in an inverse heat equation from over-specified data that the source term is only time-dependent. Some numerical examples using this approach are presented and discussed.