مجله پژوهش فیزیک ایران
سال هفتم شماره 3 (پاییز 1386)

In this article we first introduce the weighted density approximation (WDA) to study the classical inhomogeneous system such as inhomogeneous fluids. Then we introduce the modified weighted density approximation (MWDA) to calculate the structure and thermodynamical properties of the FCC hard sphere crystal. The MWDA is a self consistent method where the free energy is expressed as an unperturbed expression. Usually the required input is the Percus-Yevick (PY) direct correlation function of hard sphere. In addition to this, we use the hard sphere DCF introduced by Roth et al. [J. Phys. Condense Matter, 14, 12063 (2002).], here we call it RELK, we also introduce a new expression for the DCF which is a combination of the PY and RELK. This new expression gives the best result for the DCF of hard sphere, as it compared with the Monte Carlo simulation. In our calculation we use all these DCFs to calculate the free energy and freezing parameters of FCC hard sphere crystals. Although we obtained the better results using the PY-RELK DCF but it seems we should improve the MWDA to get better result.

The energy levels of deformed nuclei could be determined by Nilsson model. In this model the deformation of a nucleus has an axial symmetry, but we have considered the energy levels of a non-spherical nucleus as an elliptic form, and solved it by a degenerate first order perturbation method. The original Hamiltonian is a mixture of Spherical Shell Model Hamiltonian and a perturbation term. We have solved this Hamiltonian with the quantum numbers corresponding to Nilsson model-parameters and deformed 3-axial model for the values of, then we obtained the corresponding energy levels and plot them.

Level crossing is a powerful method for analyzing the random time series. In this paper by introducing this method we investigate the beta noises and represent differences between 1/f noise and white noise and also research the cardiac heart interbeat interval (RR) time series and find clear distinctions between healthy samples and samples with Congestive heart failure (CHF) disease.

The Boltzmann equation is a semiclassical approach to the calculation of the electrical conductivity. In this work we will first introduce a simple model for calculation of thin film resistivity and show that in an appropriate condition the resistivity of thin films depends on the electron mean free path, so that studying and measurement of thin films resistivity as a function of film thickness would lead to calculation of the electron mean free path in the films. Ni single layers and Ni/Cu multilayers were grown using electrodeposition technique in potentiostatic mode. The films also characterized using x-ray diffraction technique and the results show at least in the growth direction, the films were grown epitaxially and follow their substrate textures.

A method is presented to reduce the singular Lippmann-Schwinger integral equation to a simple matrix equation. This method is applied to calculate the matrix elements of the reaction and transition operators, respectively, on the real axis and on the complex plane. The phase shifts and the differential scattering amplitudes are computable as well as the differential cross sections if the R- and/or T-matrix elements on the energy-shell are known. The method is applicable by using the Gaussian quadratures based on the Legenre, Laguer Chebyshev and shifted Chebyshev polynomials. Choosing the nodal points and weight functions depends on the aspects of the problem.

Work function and surface energy per unit area were calculated in the framework of density functional theory (DFT) with Linearized A ug mented Plane Wave Plus Local Orbital method in full potential for a clean symmetric slab of silicon containing two (top and bottom) surfaces. The surfaces were theoretically modeled using supercell technique by stacking a variety of silicon layers along (111) crystallographic direction. In order to make the slab symmetric, two equivalent amounts of vacuums were added on the top and bottom of the Si(111) surfaces. In order to simulate the interface between lead and silicon, thin films of Pb were deposited on the prepared Si(111) surfaces. The calculations were performed in the absence and presence of spin-orbit coupling (SO) for the three phases of top site, T1, and fcc, T4, as well as hcp, H3. Our calculated total energies in agreement with experimental measurements show that the T1 phase, for which Pb atom is located along the Si atom of the first silicon layer, is the most stable phase. For the interface of Pb/Si(111) work function and energy formation were then calculated obtaining the most stable top site phase into account. The Si-Pb bond in the interface has been determined to be sigma.

Band structure of porous alumina photonic crystal in the Γ X direction was calculated using order-N method. In a comparison of calculated results with experimental data of reflective and absorptive index, the variation of refractive index of alumina in the external region of oxide layer, around the pores were studied. A Gaussian distribution function was adopted for phosphate anions in the external oxide layer and the variation of refractive index and diffusion depth were determined. The structure of the first four bands was calculated using the obtained distribution of refractive index in the external oxide layer for both TE and TM mode. This results show a narrow full band gap in the TM mode.