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Habibi M.,Islamic Azad University at Shirvan | Ghamari F.,Islamic Azad University
Physics of Plasmas | Year: 2011

The non-stationary self-focusing of high intense laser beam in under-dense plasma with upward increasing density ramp is investigated. The obtained results show that slowly increasing plasma density ramp is very important in enhancing laser self-focusing. Also, the spot size oscillations of laser beam in front and rear of the pulse for two different density profiles are shown. We have selected density profiles that already were used by Sadighi-Bonabi Phys. Plasmas 16, 083105 (2009). Ramp density profile causes the laser beam to become more focused and penetrations deeps into the plasma by reduction of diffraction effects. Our computations show more reliable results in comparison to the previous works. © 2011 American Institute of Physics.

Bayat M.,Islamic Azad University at Shirvan | Pakar I.,Islamic Azad University at Shirvan
Latin American Journal of Solids and Structures | Year: 2011

A vast amount of published work can be found in the field of beam vibrations dealing with analytical and numerical techniques. This paper deals with analysis of the nonlinear free vibrations of beams. The problem considered represents the governing equation of the nonlinear, large amplitude free vibrations of tapered beams. A new implementation of the ancient Chinese method called the Max-Min Approach (MMA) and Homotopy Perturbation Method (HPM) are presented to obtain natural frequency and corresponding displacement of tapered beams. The effect of vibration amplitude on the non-linear frequency is discussed. In the end to illustrate the effectiveness and convenience of the MMA and HPM, the obtained results are compared with the exact ones and shown in graphs and in tables. Those approaches are very effective and simple and with only one iteration leads to high accuracy of the solutions. It is predicted that those methods can be found wide application in engineering problems, as indicated in this paper.

Bayat M.,Islamic Azad University at Shirvan
International Journal of Physical Sciences | Year: 2011

In this paper, He's variational approach method is used to solve large amplitude free vibration of a mass grounded by linear and nonlinear springs in series. The conservative oscillation system is formulated as a nonlinear ordinary differential equation having linear and nonlinear stiffness components. By doing some simple mathematical operations on this method, we can obtain their natural frequencies. The main objective of present study is to obtain highly accurate analytical solution, which is valid for whole solution domain, for free vibration of a conservative oscillator with inertia and static type cubic nonlinearities. Other numerical results are finally presented and discussed to validate the present analysis. © 2011 Academic Journals.

Ghasemi E.,Islamic Azad University at Shirvan | Bayat M.,Islamic Azad University at Shirvan
International Journal of Physical Sciences | Year: 2011

An analytic study has been carried on steady MHD flow and heat transfer in a visco-elastic fluid flow over a semi-infinite, impermeable and non-isothermal stretching sheet with internal heat generation/absorption in the presence of radiation. Thermal conductivity is assumed to vary linearly with temperature. The governing partial differential equations are converted into ordinary differential equations by a similarity transformation. These equations are solved by homotopy analysis method (HAM). The results are then compared with numerical ones which showed excellent agreement. The temperature profiles are shown graphically for different physical parameters. © 2011 Academic Journals.

Pakar I.,Islamic Azad University at Shirvan | Bayat M.,Islamic Azad University at Shirvan
International Journal of Physical Sciences | Year: 2011

This paper applied He's energy balance method (EBM) to solve the non-natural vibrations and oscillations. We find that this method (EBM) works very well for the whole range of initial amplitudes and does not demand small perturbation and also sufficiently accurate to both linear and nonlinear physics and engineering problems. We consider a high nonlinear single degree of freedom to illustrate the effectiveness and convenience of the method. He's energy balance method as approximate method and Runge-Kutta's (RK) algorithm was also implemented to solve the governing equation through a numerical method. Finally, the accuracy of the solution obtained by the approximate method (EBM) has been shown graphically and compared with that of the numerical solution. © 2011 Academic Journals.

Bayat M.,Islamic Azad University at Shirvan | Pakar I.,Islamic Azad University at Shirvan
International Journal of Physical Sciences | Year: 2011

This paper deals with application of a new kind of analytical technique for a non-linear problem called the He's Energy Balance Method (EBM). This methodology has been utilized to achieve approximate solutions for nonlinear free vibration of conservative thick circular sector slabs. In Energy Balance Method, contrary to the conventional methods, only one iteration leads to high accuracy of solutions. These solutions do not only have high degree of accuracy, but are also uniformly valid in the whole solution domain. EBM operates very well in the whole range of the parameters involved. Excellent agreement of the approximate frequencies and periodic solutions with the exact ones could be established. Some patterns are given to illustrate the effectiveness and convenience of the methodology. It has been indicated that the numerical results of other methods have same conclusion; while EBM is much easier, more convenient and more efficient than other approaches. The Energy Balance Method is a novel method which alleviates drawbacks of the traditional numerical techniques. © 2011 Academic Journals.

Neshat M.,Islamic Azad University at Shirvan
Neural Computing and Applications | Year: 2013

Conventional particle swarm optimization (PSO) is an appropriate optimization method, yet it suffers from some drawbacks. Trapping in local minimums or premature convergence of particles leads to unsatisfactory levels of optimization. In this paper, a new method for improving PSO is provided. In the proposed method (FAIPSO), the acceleration coefficients c 1 and c 2 are adaptively adjusted for each particle in each iteration. For the adaptive controlling of the acceleration coefficients, a fuzzy inference system is used. This fuzzy inference system comprises six inputs, two outputs, and ten rules. In order to reduce inertia weight (ω), a parabolic model is used. In addition to this, a range of vision (Mu) is defined for each of the particles and every one of the particles searches within this range. This range of vision changes adaptively. In order to adaptively control the range of vision, a fuzzy inference system is employed. This system has two inputs, one output, and 14 rules. To test the proposed method, 16 benchmarks, each inheriting special characteristics, are used. The performance of the proposed method was compared with that of ten types of PSOs (each of which are among the reputable works of the PSO subject). According to the results, the proposed method shows a good performance and is more appropriate than other methods. © 2012 Springer-Verlag London.

Mahdi E.,Islamic Azad University at Shirvan
Journal of Craniofacial Surgery | Year: 2012

Background: Anthropometry is the biologic science of human body measurement. Craniofacial anthropometry discusses the characteristics on the measures of different soft and hard tissues of the head and face, and it is considered an important paraclinical record for the growth and development of the index and also for the diagnosis and curing orthodontic matters. Studying the craniofacial anthropometrics ratios is very useful in sciences such as dentistry, medicine, maxillofacial surgery, growth and development studies, plastic surgery, bioengineering, and nonmedical branches such as respiratory equipment and eye-glasses industries. OBJECTIVES: The aims of this study were to determine Iranian cranial and facial anthropometric ratios and compare anthropometric ratios between Iranian and Canadian populations. Methods: This cross-sectional analytical study was done randomly on 564 four-to-eleven-year- old boys from Shirvan (North Khorasan, Iran) with normal face patterns. Facial and cranial ratios were estimated and compared. Data were analyzed by SPSS software. The mean values of these parameters were calculated .Finally, the regression line and the growth coefficient were determined for each parameter. Furthermore, the mean anthropometric measurement of Iranians was compared with Canadians. Student t test was used for comparing the measured values. Results: Iranian population when born has hypereuryprosopic face and hypercephalic cranium form. While getting older, the midface height increases, face becomes more prominent, chin becomes shorter, and the face and cranium change to eurycephalic and hyperleptoprosopic form, respectively. Comparison of results related to the face and cranium size between Iranian and Canadian boys (4-11 years old) showed that many craniofacial ratios have significant differences (P < 0.05). Conclusions: Approximately, all of the anthropometric measurements in Iranian population and Canadians were significantly different. Considering the significant difference in the facial and cranial anthropologic ratios and size among Iranians and Canadians, the results obtained from Canadians should not be applied as criteria for treatment plans. Because of the wide population affinity combinations in Iran, more studies, with wider variations, should be conducted among different Iranian population affinity. Copyright © 2012 by Mutaz B. Habal, MD.

Habibi M.,Islamic Azad University at Shirvan | Ghamari F.,Islamic Azad University
Physics of Plasmas | Year: 2012

By using a transient density profile, we have demonstrated stationary self-focusing of an electromagnetic Gaussian beam in cold quantum plasma. The paper is devoted to the prospects of using upward increasing ramp density profile of an inhomogeneous nonlinear medium with quantum effects in self-focusing mechanism of high intense laser beam. We have found that the upward ramp density profile in addition to quantum effects causes much higher oscillation and better focusing of laser beam in cold quantum plasma in comparison to that in the classical relativistic case. Our computational results reveal the importance and influence of formation of electron density profiles in enhancing laser self-focusing. © 2012 American Institute of Physics.

Habibi M.,Islamic Azad University at Shirvan | Ghamari F.,Islamic Azad University at Shirvan
Physics of Plasmas | Year: 2014

The results of a numerical study of high-intensity X-ray laser beam interaction with warm quantum plasma (WQP) are presented. By means of an upward ramp density profile combined with quantum factors specially the Fermi velocity, we have demonstrated significant relativistic self-focusing (RSF) of a Gaussian electromagnetic beam in the WQP where the Fermi temperature term in the dielectric function is important. For this purpose, we have considered the quantum hydrodynamics model that modifies refractive index of inhomogeneous WQPs with the inclusion of quantum correction through the quantum statistical and diffraction effects in the relativistic regime. Also, to better illustration of the physical difference between warm and cold quantum plasmas and their effect on the RSF, we have derived the envelope equation governing the spot size of X-ray laser beam in Q-plasmas. In addition to the upward ramp density profile, we have found that the quantum effects would be caused much higher oscillation and better focusing of X-ray laser beam in the WQP compared to that of cold quantum case. Our computational results reveal the importance of the use of electrons density profile and Fermi speed in enhancing self-focusing of laser beam. © 2014 AIP Publishing LLC.

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