JOURNAL OF PHYSICS MOLECULAR & ATOMIC
Year:2010 | Volume:1 | Issue:2|Papers Count:8

TiO2 nanoparticles were synthesized in Anatase and Rutile phases by Sol-Gel method and then were introduced in the Arc Discharge System which contained nitrogen atmosphere. The samples which were produced by the effect of nitrogen atmosphere, changing of N2 pressure, currents and the Arc Discharge electrode were investigated by back-scattering Raman spectroscopy, X-Ray Diffraction and Scanning Electron Microscope. Doping of nitrogen in the structure of substance has been recognized as the factor of broadening and shifts of the Raman active modes.

Residual heat removal system starts operating after the reactor shut down due to an accident or at the normal operation for the fuel reloading or because of the regular maintenance. Those are taken into account among the emergency core cooling system (ECCS) duties. In this work, a novel technique has been offered for the effective core cooling of power portable reactors, which is based on the thermal exchange between hot coolant and cryogen bath. The optimum mixture of ethylene glycol and carbonic powder creates an equilibrium low temperature bath which enables us to drop the hot water temperature down to desired stable temperature. It depends on the operating permanents such as the volumetric ratio of fluids to be cooled to the coolant (VR), initial temperature of hot water, flow rate and dry ice loading.

Thermal effects induced in Nd: Glass laser disks after optical pumping, have been studied by means of an optical interferometer. For this mean, two configurations with seven and one laser disks at Brewster angle pumped with four flash lamps and a total charging energy 3.1 kJ and 1.8 kJ, respectively. The investigation of interferometer fringes indicated that three regions exist in time domain: vibration and radiation absorption until the ending of optical pumping, vibration and heat conduction until ceasing of  mechanical vibration generated from  the flash lamps shock waves, and finally, disks heating and cooling by convection and conduction mechanisms. The regions terminate 1 ms, 10 ms and at least 1 minute after initiation of the flash lamps discharge current. The first region, depends on the flash lamps discharge circuit, and for the two other regions, vibration and heating are the main mechanisms which depend on thermal properties of the glass disks, installation techniques and cooling.

This study has been performed by using Sahand plasma focus facility and TLD dosimeters. The anisotropy in X-ray production and the absorbed x-ray dose, due to the two normal operational days, were measured. The study showed that, either the X-ray production is isotropic or the anisotropy is so low so that it could not be measured by this kind of dosimeters. In addition, the measured absorbed dose showed that the 2 mm thick iron wall (or iron shield) which is placed around the plasma focus device, has a considerable roll in decreasing the absorbed dose. This shield reduced the absorbed dose by a factor of about 60%.

In this paper, we present an analytical calculation on optical properties of graphite in the range of low-energy photons, which is detected by the p-electron transitions. Band structure of graphite is investigated using the tight-binding method with the nearest-neighbor interaction. The interaction of different layers is ignored in this study. In addition, a simple equation is obtained for electronic density of states and optical conductivity. The imaginary part of dielectric constant of graphite is calculated numerically and we show that the results are in good agreement with experimental data.

The most generally reaction-diffusion model on a Cayley tree with nearest neighbor interaction is introduced and considered through the empty interval and full interval methods in the stationary and dynamics configurations. At first for this model, the evolution equation of the system is produced in closed form. Then evolution of this system is considered by analytical approach and numerical solution with explicit finite differences method. Finally, comparing the results of analytical with numerical approaches is studied.

In this paper dependence of erbium-doped fiber amplifier (EDFA) gain on fiber length and radius of core, ion concentration and dopant profile is studied theoretically at high concentration regime. At the first step the optimization has been done on the core radius by simultaneous numerical calculation of rate equations, pump and signal equations at small signal regime and for step profile concentration. Due to numerical results, a linear relation between the optimum fiber length and optimum concentration is derived which could be helpful for designing an EDFA whit high performance. At the second step the dependence of gain on the erbium ion concentration profile is evaluated. It is shown that the use of Gaussian profile that is suggested in this paper, not only improves the gain of fiber amplifier, particularly at high concentration, but also the optimum length of EDFA doesn’t increase which is desirable for optical integrated devices. Modeling has been done by numerical calculation of the rate equations of ions, pump and signal wave equations in a self consistent manner and in the steady state. Up conversion effect has been considered by an additional term in rate equation of ion concentration.

In this paper, some different statistical growth models have been simulated on regular (square, triangular and hexagonal) and random (Voronoi) lattices. It has been showed that design of substrate doesn’t affect the growth universal class, but only changes the roughness of the growth surface.