مجله پژوهش فیزیک ایران
سال دوم شماره 4 (زمستان 1379)

Porous silicon (PS) layers come into existance as a result of electrochemical anodization on silicon. Although a great deal of research has been done on the formation and optical properties of this material, the exact mechanism involved is not well-understood yet. In this article, first, the optical properties of silicon and porous silicon are described. Then, previous research and the proposed models about reflection from PS and the origin of its photoluminescence are reveiwed. The reflecting and scattering, absorption and transmission of light from this material, are then investigated. These experiments include,different methods of PS sample preparation their photoluminescence, reflecting and scattering of light determining different characteristics with respect to Si bulk.

Recently a new process has been suggested by Froelich and Wallenius in μ CF. They predicted a high rate of formation of an excited meta-stable in the collision of excited tμ(2s) with D2, which will then decay into dμ (1s). It produces the reversing transfer channel. In this paper, we establish a new approach in study of determination of q1sand p1sparameters, where p1s is the fractional population of p1s the dμ(1s). We have shown if the meta-stable molecule is considered, p1sshould be used instead of q1sin calculations. We solved the kinetic equations for the chain reactions of μ CF in D/T mixture. Then we explored the total sticking coefficient. Regarding the solving of the kinetic μ CF of, we have determined the crucial parameters of μ CF with and without considering the meta-stable molecules, such as q1s, p1s, total sticking coefficient, fusion yield per muon and cycling rate. They were compared with experimental results. Finally we optimize the condition of temperature, density and concentration of hydrogen isotopes to increase the fusion yield of μ CF.

The weighted density functional theory proposed by Tarazona is applied to study the solid-liquid interface. In the last two decades the weighted density functional became a useful tool to consider the properties of inhomogeneous liquids. In this theory, the role of the size of molecules or the particles of which the matter is composed, was found to be important. In this resarch we study a hard sphere fluid beside a hard wall. For this study the liquid is an inhomogeneous system. We use the definition of the direct correlation function as a second derivative of free energy with respect to the density. We use this definition and the definition of the weighting function, then we minimize the grand potential with respect to the density to get the Euler Lagrange equation and we obtain an integral equation to find the inhomogeneous density profile. The obtained density profile as a function of the distance from the wall, for different bulk density is plotted in three dimensions. We also calculate the pressure and compare it with the Carnahan-starling results, and finally we obtained the surface tension at liquid-solid interface and compared it with the results of Monte Carlo simulation.

In this study time-dependent and spherically symmetric solutions of the Einstein field equations in an anisotropic background with a purely radial tension are presented. There exist three classes of solutions,1) An open spacetime with a wormhole at its center. 2) A conical spacetime. 3) A closed spacetime. These inhomogeneous solutions are reduced to FRW spacetimes in matter-dominated era, asymptotically. Therefore, they can be used to describe local inhomogeneities that are not considered in the standard model. For the wormhole solution. it is explicity shown that the considered matter is non-exotic, that is, it does not violate the energy conditions. Also, static solutions are studied. There is only one static solution,a conical spacetime. In this case, the matter satisfies the energy condition critically.

The poling process of polymers doped with chromophores is of great importance for the nonlinear properties of these materials. So, after having optimized the poling condition the second harmonic generation (SHG) was measured for PMMA polymer doped with Disperse Red 1. The dependence of SHG intensity to the poling voltage and poling temperature have been experimentally studied. The relaxation of dopant orientation in the polymer matrix was also measured.

Here we concern ouraelves with the derivation of a system of evolution equations for slowly varying amplitude of a baroclinic wave packet. The self-induced transparency, Sine-Gordon, and nonlinear Schrodinger equations, all of which possess soliton solutions, each arise for different inviscid limits. The presence of viscosity, however, alters the form of the evolution equations and changes the character of the solutions from highly predictable soliton solutions to unpredictable chaotic solutions. When viscosity is weak, equations related to the Lorenz attractor equations obtain, while for strong viscosity the Ginzburg-Landau equation obtain.