JOURNAL OF SCIENCES (ISLAMIC AZAD UNIVERSITY)
Year:2003 | Volume:13 | Issue:47|Papers Count:9

The recent observational data are strongly in favor of a positive acceleration of the present universe. In a first approximation, the background space-time that we live in, might be considered as a de Sitter space-time. If this is so, it is important to understand how quantum gravity and should formulated in de Sitter space. We discusses the some properties of linear quantum gravity necessitated to the indefinite metric quantization for preserving the de Sitter invariant and eliminating the infrared divergence in the graviton two points function. There appears two different types of negative norm states. The first one is similar to those non physical states dual to gauge states which appear in gauge quantum field theory in Minkowski space. The other is due to the occurrence of negative frequency solutions in order to preserve de Sitter covariance. This is similar to the case of minimally coupled scalar field in dS space. We discuss the possibility of generalization to the Minkowskian limit and their consequences in the renormalization theory.

A simple two dimensional model of thin film growth based on the ballestic aggregation of hard disks is proposed. In this model the impinging hard disks travel in straight line and initially "stick" to the first previously deposited hard disk they contact. Previously (Dirks and Leamy (1977)) (1) the criterion for relaxation has been migration of the impinging disk to the nearest pocket formed by two additional disks. In this model, however, relaxation is dependent on the surrounding geometry of the previously deposited atoms. The deposited disk may "relax" into a position where it then contact three, two or one previously deposited disk(s). Zone I region which is mainly influenced by shadowing effects with limited adatoms diffusion is simulated. The influence of deposition rate, self-shadowing effect, substrate roughness including amorphous substrates were investigated. Results are in good agreement with the Structure Zone Model (SZM) predictions for thin metallic films.

In the CT -6B Tokamak MHD activities detected by a poloidal array of external Mirnov coils. The start of MHD oscillation varies by changing plasma current, plasma horizontal displacement and gas pressure. During current rise, plateau and ramp down phases, polar plots of Mirnov array signals are compared with safety factor qa=5a2Bt/RIp near limiter which calculated at two different plasma radius "a" and (a-Delta x). Fourier analyses in the time and spatial domains were performed to obtain the mode number and their frequencies. Study of 3-Dimension of plotting of the time evolution of poloidal angular dependence of the amplitude of perturbed magnetic field done, it seems that there are different kinds of islands located inner and outer of a magnetic surface and they rotate at different velocities.

A model describing multiphoton dissociation of SF6 isotopes by a CO2 laser based upon the rate equations is developed. The equations are solved for the population change of molecular levels which provide insight into the dissociation process. A comparison of the results of experiments with the theoretical prediction of the model is presented.

ODCR has proven to be a highly sensitive technique for measuring the effective masses of semiconductors at microwave frequencies. The technique has shown many advantageous over conventi9nal types of cyclotron resonance measurements. The condition for well defined cyclotron resonance is ωcT>>1, where ωδ is the cyclotron frequency and is the (momentum) scattering time. The current work extends the technique to far infrared frequencies, exploiting the much greater ωcT values associated with the higher frequencies being used.

The effect of RHF (resonant helical field) on electron thermal conductivity behaviour and plasma transport has been studied in the IR- T1 tokamak. The phase shift analysis is considered in the electron thermal conductivity measurement The RHF can amplify the sawtooth oscillations. The results show a decrease in the electron thermal conductivity, xe, and also in anomalous transport. The amplification of sawtooth oscillations, the decrease in electron thermal conductivity, and the anomalous transport are verified by experiments.

A study has been made to find the effects of ion bombardment at the Cui A1203 interface using different Ar+ energies. Cu films on alumina were prepared by a cylindrical magnetron sputtering system. Crystallographic structure and the surface morphology of the films were characterized with X-ray diffraction and scanning electron microscopy (SEM), respectively. The analysis of the elements distribution was performed using Rrtherford backscattering spectroscopy (RBS), and the adhesion test had been made by pin pull test. Experimental results show that increasing the argon ion energy enhances adhesion. This effect seems to be due to ion beam mixing and more Cu-substrate contact area, as confirmed by RBS and SEM results.

The Mie theory for the light scattering from spherical particles is re-studied. Because of the importance of this theory for practical reasons (e. g., in calibrating instruments used in particle sizing), investigations are carried out, and the origin of oscillations in the scattered intensity curve as a function of particle size, as well as damping down effect of the imaginary part of the refractive index are pointed out.