سال:1393 | دوره: | شماره: |تعداد مقالات:8

The Rayleigh-Taylor instability of a heavy fluid supported by a lighter one is investigated, with the suspended dust particles and small uniform general rotation.The fluids are assumed to be incompressible. The solutions of the linearized equations of motion using the boundary conditions lead to deriving the dispersion equation in complex formula. The real formula of dispersion relation has been analyzed and the behavior of growth rate with respect to the suspended dust particles and components of rotation have been examined. The results show that relaxation frequency of the suspended particles beside the general rotation will bring about more stability on the growth rate of unstable configuration.

An analytical and numerical study is made on the dispersion properties of a cylindrical waveguide filled with plasma. An electron beam and static external magnetic field are considered as the mechanisms for controlling the field attenuation and possible stability of the waveguide.The effects of plasma warmness and inhomogeneity are also considered. Dispersion relations in w describing different physical situations that govern the mode propagation in the waveguide are obtained. The plasma dielectric tensors and the dispersion relations which describe E and H waves and, hence, the damping rate of these waves are calculated and studied. The necessary conditions for the field stability in the waveguide and amplification coefficients for these waves are also obtained. H-wave modes are always attenuated by collisional effect. The growth of the excited E wave is calculated in the resonance case, and the stability condition for the E wave is obtained. E waves are found to be more stable in warm plasma compared to cold plasma. The results obtained here are of great interest and may be used to analyze how the plasma affects the electromagnetic properties of the cavity of the 1-2 MW 140-170 GHz continuous-wave gyrotron (for W7-X stellarator and ITER), for MW gyrotron development for fusion plasma applications, and for second harmonic generation in a plasma-filled parallel plane waveguide.

Fibonacci fractal structures have been already studied. However, more special fractal structures could be beneficial in specific applications. In this paper, we create three variations of Fibonacci fractal photonic crystals as well as original structure, including: inverse Fibonacci fractal photonic crystal, mirror symmetry Fibonacci fractal photonic crystal (MSFFPC), and finally folded Fibonacci fractal photonic crystal. The transmission spectra of these structures are simulated and analyzed. Our findings show that presented structures have their own characteristics, therefore, can be used for different applications according to required specifications. Some MSFFPC structures, for instance, could be used to develop resonant microcavities with high Q factor that can be applicable in design and construction of ultrasensitive optical sensors with very high quality factor requirements. The narrower resonance peaks and the smaller amount of interfaces lead to a higher sensitivity for this structure.

spin-isospin dependent three-dimensional approach has been applied for the formulation of the threenucleon bound state, and a new expression for Faddeev equation based on three-nucleon free basis states has been obtained.The advantage of this new expression is that the Faddeev integral equation has been simpler for numerical calculation.

This paper is an attempt to compare the influence of various annealing conditions on growth, nanostructure, surface morphology and electrical properties of copper oxide thin films. Cu thin films of 85 nm thickness were deposited on glass substrate by thermal evaporation method, and then post-annealed at different environments (air and oxygen flow), different temperatures (200–400oC) and different times (35 and 75 min). X-ray diffraction results showed (Cu2O) cuprite phase for all annealed samples at 200 and 250oC and (CuO) tenorite phase for all samples annealed under different conditions at 350 and 400oC. A complex phase of CuO and Cu2O was observed for all annealed samples at 300oC, with exception for the sample annealed with flow of oxygen for 75 min. The atomic force microscopy results showed that surface morphology of the samples was strongly affected by the changes of annealing conditions (i.e., time, temperature and environment). The size of the grains increased with annealing temperature and time, while the samples annealed with oxygen flow showed larger grains than those annealed in air. Two different behaviors with annealing temperature were distinguished for the surface roughness of the samples annealed in the air and those annealed with flow of oxygen. Resistivity and Hall effect of samples were measured by a four-point probe instrument and a Hall effect investigation system, respectively. The electrical analyses showed that the variations in annealing conditions had a remarkable effect on measured electrical parameters, namely films resistivity, carriers concentration and type, and Hall mobility.

Accelerator-driven systems are extensively developed to generate neutron sources for research, industrial and medical plans. Different heavy elements are utilized as spallation targets to produce spallation neutrons.Computational methods are efficiently utilized to simulate neutronic behavior of a spallation target. MCNPX 2.6.0 is used as a powerful code based on Monte Carlo stochastic techniques for spallation process computation. This code has the ability to transport different particles using different physical models. In this paper, MCNPX has been utilized to calculate the leaked neutron yield from Pb, LBE, W, Ta, Hg, U, Th, Sn and Cu cylindrical heavy targets. Effects of the target thickness and diameter on neutron yield value have been investigated via the thickness and diameter variations between 5–30 and 5–20 cm, respectively. Proton-induced radionuclide production into the targets as well as leaked neutron spectra from the targets has been calculated for the targets of an optimum determined dimension.1 GeV proton particle has been selected to induce spallation process inside the targets.2 mm spatial FWHM distribution has been considered for the 1 mA proton beam.Uranium target produced the highest leaked neutron yield with a 1.32–3.7 factor overweigh the others. Dimension of 159 60 cm is suggested for all the cylindrical studied spallation targets. Th target experienced the highest alpha emitter radionuclide production while lighter elements such as Cu and Sn bore the lowest radio-toxicity. LBE liquid spallation target competes with the investigated solid targets in neutronic point of view while has surpass than volatile liquid Hg target.

A motivation for using fuzzy systems stems in part from the fact that they are particularly suitable for processes when the physical systems or qualitative criteria are too complex to model and they have provided an efficient and effective way in the control of complex uncertain nonlinear systems. To realize a fuzzy model-based design for chaotic systems, it is mostly preferred to represent them by T–S fuzzy models. In this paper, a new fuzzy modeling method has been introduced for chaotic systems via the interval type-2 Takagi–Sugeno (IT2 T–S) fuzzy model. An IT2 fuzzy model is proposed to represent a chaotic system subjected to parametric uncertainty, covered by the lower and upper membership functions of the interval type-2 fuzzy sets. Investigating many well-known chaotic systems, it is obvious that nonlinear terms have a single common variable or they depend only on one variable. If it is taken as the premise variable of fuzzy rules and another premise variable is defined subject to parametric uncertainties, a simple IT2 T–S fuzzy dynamical model can be obtained and will represent many well-known chaotic systems. This IT2 T–S fuzzy model can be used for physical application, chaotic synchronization, etc. The proposed approach is numerically applied to the well-known Lorenz system and Rossler system in MATLAB environment.

Using a traveling wave reduction technique, we have shown that Maccari equation, (2+1) -dimensional nonlinear Schrodinger equation, medium equal width equation, (3+1) -dimensional modified KdV–Zakharov–Kuznetsev equation, (2+1) -dimensional long wave-short wave resonance interaction equation, perturbed nonlinear Schro¨dinger equation can be reduced to the same family of auxiliary elliptic-like equations. Then using extended F-expansion and projective Riccati equation methods, many types of exact traveling wave solutions are obtained.With the aid of solutions of the elliptic-like equation, more explicit traveling wave solutions expressed by the hyperbolic functions, trigonometric functions and rational functions are found out. It is shown that these methods provide a powerful mathematical tool for solving nonlinear evolution equations in mathematical physics. A variety of structures of the exact solutions of the elliptic-like equation are illustrated.