Islamic Azad University at Naein

www.naeiniau.ac.ir
Naein, Iran

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Koochi A.,Islamic Azad University at Naein | Noghrehabadi A.,Shahid Chamran University | Abadyan M.,Islamic Azad University
International Journal of Modern Physics B | Year: 2011

Beam-type nano-electromechanical system (NEMS) is one of the most components in constructing nano-devices. Herein, a distributed parameter model is used to study the influence of van der Waals (vdW) attraction on the pull-in performance of the cantilever NEMS. Homotopy perturbation method (HPM) is applied to solve the nonlinear governing equation of the actuators in the form of convergent series. Moreover, analytical results are compared with those of numerical method as well as a lumped parameter model. The pull-in voltage and critical cantilever tip deflection of NEMS are determined. Results depict that vdW attraction decreases the pull-in deflection and voltage of the NEMS. On the other hand, the fringing field increases the pull-in deflection while decreases the pull-in voltage of the system. The analytical results have good agreement with numerical results and those available in the literature. © 2011 World Scientific Publishing Company.


Tadi Beni Y.,Shahrekord University | Abadyan M.,Islamic Azad University | Koochi A.,Islamic Azad University at Naein
Physica Scripta | Year: 2011

In this paper, the effect of the Casimir attraction on the torsion/bending coupled pull-in instability of an electrostatic nano-actuator has been investigated for the first time. The governing equation of the actuator is derived and the instability parameters of the nano-actuator have been computed as a function of the geometrical characteristics and the bending/torsion stiffness ratio of the nano-actuator. The results reveal that the Casimir attraction could highly affect the coupled pull-in performance of the actuator. It is found that the Casimir force can reduce the instability voltage of nano-actuators. This deteriorating effect is more clearly highlighted in the torsional pull-in mode compared to the bending pull-in mode. Furthermore, it is found that the influence of the Casimir force on pull-in angle and deflection of the torsional actuator depends on the torsion/bending coupling ratio. For small-gap torsional actuators, the pull-in parameters have been strongly affected by the Casimir force, and neglecting Casimir attraction may lead to considerable error during simulations of the pull-in instability. The results of the present model are in better agreement with the experimental data compared to previous models. © 2011 The Royal Swedish Academy of Sciences.


Tadi Beni Y.,Shahrekord University | Koochi A.,Islamic Azad University at Naein | Abadyan M.,Islamic Azad University
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2011

In this paper, the static pull-in instability of beam-type nano-electromechanical systems (NEMS) is theoretically investigated considering the effect of Casimir attraction, elastic boundary conditions (BC) and size dependency. Rotational springs are utilized at each of the supported ends of the simply and doubly supported beams to model an elastic BC. The modified couple stress theory is applied to examine the size effects on the instability of nanostructures. In order to solve the nonlinear constitutive equation of nano-beams, modified Adomian decomposition (MAD) as well as the numerical method is employed. The results reveal significant influences of Casimir attraction, elastic BC and size dependency on the pull-in characteristics of NEMS. The obtained MAD solution agrees well with the numerical one. © 2010 Elsevier B.V. All rights reserved.


Koochi A.,Islamic Azad University at Naein | Kazemi A.,Islamic Azad University | Abadyan M.,Islamic Azad University
Nano | Year: 2011

Herein, the deflection and instability of a freestanding carbon nanotube (CNT) probe/sensor in the vicinity of the graphene layers are investigated. A nanoscale continuum model is employed to obtain nonlinear constitutive equation of freestanding CNT. The van der Waals attraction is computed from the simplified Lennard-Jones potential for two common engineering cases including large and small number of graphene layers. Four approaches, i.e., approximated function, homotopy perturbation method, lumped parameter model and numerical analysis, are employed to solve the governing equation of CNT. The intermolecular force-induced deflection, minimum initial gap and stable length of freestanding CNT are determined. The analytical results agree well with the numerical solutions. © 2011 World Scientific Publishing Company.


Abadyan M.,Islamic Azad University at Naein | Bagheri R.,Sharif University of Technology | Kouchakzadeh M.A.,Sharif University of Technology | Hosseini Kordkheili S.A.,Sharif University of Technology
Materials and Design | Year: 2011

In this paper, tensile strain energy absorption of two different hybrid modified epoxies has been systematically investigated. In one system, epoxy has been modified by amine-terminated butadiene acrylonitrile (ATBN) and hollow glass spheres as fine and coarse modifiers, respectively. The other hybrid epoxy has been modified by the combination of ATBN and recycled Tire particles. The results of fracture toughness measurement of blends revealed synergistic toughening for both hybrid systems in some formulations. However, no evidence of synergism is observed in tensile test of hybrid samples. Scanning electron microscope (SEM), transmission optical microscope (TOM) and finite element (FEM) simulation were utilized to study deformation mechanisms of hybrid systems in tensile test. It is found that coarse particles induce stress concentration in hybrid samples. This produces non-uniform strain localized regions which lead to fracture of hybrid samples at lower tensile loading and energy absorption levels. © 2011.


Koochi A.,Islamic Azad University at Naein | Kazemi A.S.,Islamic Azad University | Noghrehabadi A.,Shahid Chamran University | Yekrangi A.,Islamic Azad University | Abadyan M.,Islamic Azad University
Materials and Design | Year: 2011

Modeling the buckling of multi walled carbon nanotube (MWCNT) probes/actuators in the vicinity of thin and thick graphite has been carried out for the first time via two analytical approximation methods as well as a numerical one. A hybrid nano-scale continuum model based on Lennard-Jones potential is applied to simulate the intermolecular force-induced deflection of MWCNT. The critical values of MWCNT tip deflection and MWCNT-graphite attraction at the onset of the instability are computed. In addition, minimum nanotube-graphite initial gap and stable length of freestanding CNT are determined as basic parameters for engineering applications and nano-devices design. The stable length of MWCNT is determined as a function of its geometrical and material characteristics, initial gap and number of graphene layers. © 2011.


Koochi A.,Islamic Azad University at Naein | Kazemi A.,Islamic Azad University | Khandani F.,Islamic Azad University at Ahar | Abadyan M.,Islamic Azad University
Physica Scripta | Year: 2012

While surface effects often play an important role in the pull-in performance of electromechanical nano-actuators, only a few works have been conducted that take these effects into account. In this paper, the influence of surface effects including residual surface stress and surface elasticity on the pull-in instability of a cantilever nano-actuator is investigated incorporating the influence of quantum vacuum fluctuations through the Casimir attraction. An analytical closed-form solution is obtained in terms of the modified Adomian decomposition (MAD) series and the obtained results are compared with those in the literature as well as the numerical solution. The instability parameters of the actuator are determined. The results demonstrate that surface effects cause the cantilever nano-actuator to behave as a softer structure. It is found that surface effects become more significant for low values of the actuator thickness as well as high values of the initial gap/width ratio. Furthermore, the influence of surface energy on the detachment length and the minimum gap of the freestanding actuator is discussed. Interestingly, the present MAD solution provides reliable results without the shortcomings of the previously proposed homotopy perturbation method. © 2012 The Royal Swedish Academy of Sciences.


Abdi J.,Islamic Azad University | Koochi A.,Islamic Azad University at Naein | Kazemi A.S.,Islamic Azad University | Abadyan M.,Islamic Azad University
Smart Materials and Structures | Year: 2011

An electromechanical beam-type nano-actuator is one the most important smart nanostructures. In this paper, modified couple stress theory is used to model the size effect on the static pull-in instability of electrostatic nanocantilevers in the presence of dispersion (Casimir/van der Waals) forces. The monotonically iterative method (MIM) and homotopy perturbation method (HPM) are employed to solve the nonlinear constitutive equation of the nanostructure as well as numerical methods. Furthermore, a lumped parameter model is developed to explain the size-dependent pull-in performance of the nano-actuator. The basic engineering design parameters such as critical tip deflection and pull-in voltage of the nanostructure are computed. It is found that dispersion forces decrease the pull-in voltage and deflection of the nano-actuator at sub-micrometer scales. On the other hand, the size effect can increase the pull-in parameters of the nano-actuators. The results indicate that the proposed analytical solutions are reliable for simulating nanostructures at sub-micrometer ranges. © 2011 IOP Publishing Ltd.


Foroozandeh E.,Islamic Azad University at Naein | Derakhshan-Barjoei P.,Islamic Azad University | Jadidi M.,Islamic Azad University
Toxicology and Industrial Health | Year: 2013

In this study, the effect of exposure to an 8 mT, 50 Hz extremely low-frequency electromagnetic field (ELF EMF) on memory consolidation of adult male and female mice was studied. For this purpose male and female mice were randomly distributed among six groups (n = 10 in each group). Using passive avoidance task, despite its natural tendency, mouse learns to stay on a small platform to avoidant electric shock. Immediately after the learning session, laboratory animals in the experimental groups were placed in an 8 mT, 50 Hz sinusoidal EMF for 4 h. The second male and female groups were sham exposed (exposure device off) and the third groups were considered as the controls. Twenty-four hours after the learning session, the animals were placed on small platform again and step-down latency was measured as the memory consolidation index. Significant (p < 0.05) decreases were determined among groups in memory function and results showed that exposure to an 8 mT, 50 Hz EMF for 4 h has devastating effects on memory consolidation in male and female mice. © The Author(s) 2012.


Koofigar H.R.,University of Isfahan | Amelian S.,Islamic Azad University at Naein
International Journal of Innovative Computing, Information and Control | Year: 2012

This paper addresses the chaos control of uncertain chaotic nonlinear gyros with unknown parameters. In general, the underlying class of gyros may be perturbed by external disturbances with different sources. Depending on the characteristics of un¬certain parameters and disturbances, two different adaptive-based control algorithms are proposed. In the first method, an adaptive H ∞ controller is designed when the external disturbances are square-integrable. The other proposed scheme is based on developing a pure adaptive controller, in which the parameters and disturbances can be time-varying with unknown bounds. In both methods, the prescribed robustness property is guaranteed and the stability analysis is presented, using the Lyapunov stability theorem. Simulation studies show that the goal of chaos control is achieved despite the system uncertainties and external disturbances. © 2012 ICIC International.

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