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Ojaroudi N.,Islamic Azad University
Microwave and Optical Technology Letters | Year: 2014

In this article, a new design of compact ultrawideband (UWB) monopole antenna is presented.The antenna consists of a ordinary square radiating patch and a ground plane with pairs of rotated L-shaped slots and parasitic structures. By cutting a pair of rotated L-shaped slots and also by embedding a pair of rotate L-shaped conductor-backed plane in air gap distance, additional resonances are excited and much wider impedance bandwidth can be produced. Also, the usable upper frequency of the antenna is extended from 10.3 to 18.31 GHz. Simulated and measured results show that the antenna design exhibits an operating bandwidth (VSWR < 2) from 3.09 to 18.31 GHz which provides a wide usable fractional bandwidth of more than 140%. The proposed antenna has an ordinary square radiating patch, therefore, displays a good omnidirectional radiation pattern even at higher frequencies. The antenna configuration is simple, easy to fabricate, and can be integrated into UWB systems. © 2014 Wiley Periodicals, Inc.

Thanks to the brilliant mechanical properties of single-walled carbon nanotubes (SWCNTs), they are suggested as high speed nanoscale vehicles. To date, various aspects of vibrations of SWCNTs have been addressed; however, vibrations and instabilities of moving SWCNTs have not been thoroughly assessed. Herein, vibrational properties of an axially moving SWCNT with simply supported ends are studied using nonlocal Rayleigh beam theory. Employing assumed mode and Galerkin methods, the discrete governing equations pertinent to longitudinal, transverse, and torsional motions of the moving SWCNT are obtained. The resulting eigenvalue equations are then numerically solved. The speeds corresponding to the initiation of the instability within the moving nanostructure are calculated. The roles of the speed of the moving SWCNT, small-scale parameter, and aspect ratio on the characteristics of longitudinal, transverse, and torsional vibrations of axially moving SWCNTs are scrutinized. The obtained results show that the appearance of the small-scale parameter would result in the occurrence of both divergence and flutter instabilities at lower levels of the speed. © 2013 Elsevier B.V. All rights reserved.

In total, 137 goat, cow, sheep, and buffalo milk samples were collected in different regions of Iran and analysed to determine concentrations of lead and cadmium by a graphite furnace atomic absorption spectrometric method. The mean recovery of the analytical method was 96.3% and 104% for cadmium and lead, respectively. The mean lead and cadmium contents obtained from 137 samples were 1.93 ± 1.48 (range: 0.18-6.11 ng/ml) and 9.51 ± 4.93 ng/ml (range: 1.84 ng/ml-30.50 ng/ml), respectively. Lead concentration in 8.1% of sheep and 1.9% of cow milk samples was higher than the newly established Codex standard. The mean concentrations of cadmium and lead in animals aged ≤3 years (n = 80; 1.40 ± 1.05 ng/ml and 7.91 ± 3.60 ng/ml, respectively) were lower than in animals aged >3 years (n = 58; 2.69 ± 1.67 ng/ml and 11.8 ± 5.71 ng/ml, respectively). © 2012 Elsevier Ltd. All rights reserved.

Kiani K.,Islamic Azad University
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2014

The alteration of the frequencies of nanostructures via an external field is of great importance in the design of nanomechanical devices whose vibrations should be appropriately controlled. Herein, free in-plane and out-of-plane vibration behaviors of conducting rectangular nanoplates subjected to unidirectional in-plane steady magnetic fields are of concern. To this end, the body forces exerted on the nanoplate based on the hypotheses of Kirchhoff, Mindlin, and higher-order plate theories are obtained. Subsequently, the nonlocal versions of the equations of motion of the conducting nanoplate for the suggested plate models are extracted. The presented formulations show that the small-scale parameter is incorporated into the exerted forces on the nanoplate due to the applied magnetic field. For the proposed models, the frequencies pertinent to the in-plane and out-of-plane vibrations of the nanoplates are evaluated. In the continuing, the roles of the length-to-thickness ratio, length-to-width ratio, small-scale parameter, and magnetic field strength on both in-plane and out-of-plane frequencies are addressed. The capabilities of the proposed models in predicting such frequencies are also explained and discussed. © 2013 Elsevier B.V. All rights reserved.

Almasi M.,Islamic Azad University
Journal of Chemical Thermodynamics | Year: 2014

Densities and viscosities of binary liquid mixtures of formamide (FA) with polar solvents namely, 2-PrOH, 2-BuOH, 2-PenOH, 2-HexOH, and 2-HepOH, have been measured as a function of composition range at temperatures (298.15, 303.15, 308.15, 313.15) K and ambient pressure. From experimental data, excess molar volumes, VmE and viscosity deviations Δη, were calculated and correlated by Redlich-Kister type function. The effect of temperature and chain-length of the 2-alkanols on the excess molar volumes and viscosity deviations are discussed in terms of molecular interaction between unlike molecules. The statistical associating fluid theory (SAFT), and perturbed chain statistical associating fluid theory (PC-SAFT) were applied to correlate and predict the volumetric behavior of the mixtures. The best predictions were achieved with the PC-SAFT equation of state. Also the Peng-Robinson-Stryjek-Vera equation of state has been used to predict the viscosity of binary mixtures. © 2013 Elsevier Ltd. All rights reserved.

A mathematical model is proposed to explore vibrations and instabilities of moving functionally graded (FG) nanobeams. It is assumed that the FG nanobeam moves with a constant velocity and its material properties vary continuously across the thickness according to a power-law relation. The longitudinal and lateral equations of motion of the moving nanostructure are extracted by employing the nonlocal Rayleigh beam model. Using Galerkin approach and admissible mode shapes, the longitudinal and transverse frequencies are calculated. The effects of the power-law index, small-scale parameter, length of the FG nanobeam, and its velocity on the frequencies and stability of the moving nanostructure are comprehensively addressed. Both divergence and flutter instabilities of moving FG nanobeams are discussed, and the roles of influential factors on such phenomena are explained. © 2013 Elsevier Ltd.

Vakili B.,Islamic Azad University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2010

We study the classical and quantum models of a Friedmann-Robertson-Walker (FRW) cosmology, coupled to a perfect fluid, in the context of the scalar-metric gravity. Using the Schutz' representation for the perfect fluid, we show that, under a particular gauge choice, it may lead to the identification of a time parameter for the corresponding dynamical system. It is shown that the evolution of the universe based on the classical cosmology represents a late time power law expansion coming from a big-bang singularity in which the scale factor goes to zero while the scalar field blows up. Moreover, this formalism gives rise to a Schrödinger-Wheeler-DeWitt (SWD) equation for the quantum-mechanical description of the model under consideration, the eigenfunctions of which can be used to construct the wave function of the universe. We use the resulting wave function in order to investigate the possibility of the avoidance of classical singularities due to quantum effects by means of the many-worlds and ontological interpretation of quantum cosmology. © 2010 Elsevier B.V. All rights reserved.

Lateral wave propagation in an elastically confined single-walled carbon nanotube (SWCNT) experiences a longitudinal magnetic field is examined using nonlocal Rayleigh, Timoshenko, and higher-order beam theories. The SWCNT is modeled via an equivalent continuum structure (ECS) and its interaction with the surrounding elastic medium is simulated via lateral and rotational continuous springs along its length. For the proposed models, the dimensionless governing equations describing transverse vibration of the SWCNT are constructed. Assuming harmonic solutions for the propagated sound waves, the dispersion equation associated with each model is obtained. Subsequently, the explicit expressions of the frequencies as well as the corresponding phase and group velocities, called characteristics of the waves, are derived for the proposed models. The influences of the slenderness ratio, the mean radius of the ECS, the small-scale parameter, the longitudinal magnetic field, the lateral and rotational stiffness of the surrounding matrix on the characteristics of flexural and shear waves are explored and discussed. © 2012 Elsevier B.V. All rights reserved.

Kiani K.,Islamic Azad University
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2012

Vibration of a conducting nanowire embedded in an elastic matrix due to an axial magnetic shock is of concern. Based on Maxwell's and Cauchy's equations, a model is proposed to study the problem in the context of nonlocal continuum theory. For solving the equations of motion of the nanowire, an analytical approach and a semi-analytical technique are proposed for low and high levels of small-scale parameter, respectively. The effects of small-scale parameter, stiffness of the surrounding matrix, and duration of the applied magnetic shock on the maximum dynamic elastic fields are examined. © 2012 Elsevier B.V. All rights reserved.

In the context of nonlocal continuum theory, seeking an analytical solution to the equations of motion of stocky double-walled carbon nanotubes (DWCNTs) with arbitrary boundary conditions is a very problematic task. Thereby, proposing efficient numerical techniques for frequency analysis and optimal design of such nanostructures is of great advantageous. Herein, free transverse vibration of an elastically supported stocky DWCNT embedded in an elastic matrix under initial axial force is of interest. To this end, the equivalent continuum structures (ECSs) associated with the innermost and outermost tubes are taken into account. The interaction of the DWCNT with its surrounding matrix is modeled using lateral and rotary continuous springs. Through consideration of interlayer van der Waals forces via an equivalent spring system, the two tubes are appropriately interacted. Using Hamilton's principle, the dimensionless equations of motion of elastically supported DWCNTs are established using nonlocal Rayleigh, Timoshenko, and higher-order beam theories. The unknown fields of the equations of motion for each model are discretized in the spatial domain using reproducing kernel particle method. After tedious calculations, the set of eigenvalue equations pertinent to each model is extracted and numerically solved. The convergence checks of the proposed numerical models in predicting flexural frequencies of DWCNTs are carried out. The obtained results are also compared with those of other works and a reasonably good agreement is achieved. Through various numerical studies, the influences of slenderness ratio, ratio of the mean radius to the thickness of the ECSs, small-scale parameter, initial axial force, lateral and rotational stiffness of the surrounding matrix on the flexural frequencies of stocky DWCNTs are carefully examined for different boundary conditions. The capabilities of the proposed nonlocal models in capturing the flexural frequencies of stocky DWCNTs are discussed as well. © 2012 Elsevier Ltd.

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