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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. Source


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. Source


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. Source


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. Source


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. Source

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