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Khadem, M.,Penkov, O.V.,Pukha, V.E.,Maleyev, M.V.,Kim, D.E. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.80 No.-
The wear resistance and optical properties of ultra-thin diamond-like carbon (DLC) coatings deposited on glass substrates at room temperature were investigated. The coatings were deposited using a C<SUB>60</SUB> ion beam. A sequence of surface treatments including ion-beam etching, molecular-beam deposition and ion-beam deposition were used for production of ultra-thin DLC coatings with a nano-patterned surface. The goal of the surface nano-patterning was to improve the wear resistance of the DLC coatings while maintaining a low thickness to obtain a high optical transparency. The experimental results demonstrated the excellent ability of the ultra-thin DLC coatings to improve the wear resistance of the glass substrates. A comparison between the wear rate for the DLC coating with nano-patterns and that of a more smooth coating revealed that the nano-patterned surface shows a 39% higher wear resistance. Furthermore, the coatings demonstrated a high transparency (94-97%) in the visible-light wavelength range.
S.M. Jebreiil Khadem,Y. Abdi,S. Darbari,F. Ostovari 한국물리학회 2014 Current Applied Physics Vol.14 No.11
Graphene/ZnO hybrid was used, for the first time, to fabricate a highly selective and sensitive graphene based gas sensor by a combination of electromechanical and electrochemical characteristics of the graphene. ZnO nanowires in our fabricated sensor have two important roles: as the reductant of graphene oxide to obtain graphene and as an efficient electromechanical actuator due to their piezoelectric properties. To investigate the operation of the fabricated sensor as a gas sensor, a selected set of chemical vapors were introduced to the structure. It was found that chemical vapors change the resonance frequency of the graphene/ZnO structure, as well as the electrical resistivity of the sensor. The observed variation of the mechanical and electrical characteristics of the graphene/ZnO in response to gas exposure entitles the graphene/ZnO based sensor as a highly selective/sensitive device for gas sensing applications with distinctive signatures for different gas species.
Nonlinear response of a resonant viscoelastic microbeam under an electrical actuation
M. Zamanian,S.E. Khadem,S.N. Mahmoodi 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.35 No.4
In this paper, using perturbation and Galerkin method, the response of a resonant viscoelastic microbeam to an electric actuation is obtained. The microbeam is under axial load and electrical load. It is assumed that midplane is stretched, when the beam is deflected. The equation of motion is derived using the Newton's second law. The viscoelastic model is taken to be the Kelvin-Voigt model. In the first section, the static deflection is obtained using the Galerkin method. Exact linear symmetric mode shape of a straight beam and its deflection function under constant transverse load are used as admissible functions. So, an analytical expression that describes the static deflection at all points is obtained. Comparing the result with previous research show that using deflection function as admissible function decreases the computation errors and previous calculations volume. In the second section, the response of a microbeam resonator system under primary and secondary resonance excitation has been obtained by analytical multiple scale perturbation method combined with the Galerkin method. It is shown, that a small amount of viscoelastic damping has an important effect and causes to decrease the maximum amplitude of response, and to shift the resonance frequency. Also, it shown, that an increase of the DC voltage, ratio of the air gap to the microbeam thickness, tensile axial load, would increase the effect of viscoelastic damping, and an increase of the compressive axial load would decrease the effect of viscoelastic damping.
M. H. Ghayesh,S. E. Khadem 국제구조공학회 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.27 No.1
The main source of transverse vibration of a conveyor belt is frictional contact between pulley and belt. Also, environmental characteristics such as natural dampers and springs affect natural frequencies, stability and bifurcation points of system. These phenomena can be modeled by a small velocity fluctuation about mean velocity. Also, viscoelastic foundation can be modeled as the dampers and springs with continuous characteristics. In this study, non-linear vibration of a conveyor belt supported partially by a distributed viscoelastic foundation is investigated. Perturbation method is applied to obtain a closed form analytic solutions. Finally, numerical simulations are presented to show stiffness, damping coefficient, foundation length, non-linearity and mean velocity effects on location of bifurcation points, natural frequencies and stability of solutions.
Nonlinear response of a resonant viscoelastic microbeam under an electrical actuation
Zamanian, M.,Khadem, S.E.,Mahmoodi, S.N. Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.35 No.4
In this paper, using perturbation and Galerkin method, the response of a resonant viscoelastic microbeam to an electric actuation is obtained. The microbeam is under axial load and electrical load. It is assumed that midplane is stretched, when the beam is deflected. The equation of motion is derived using the Newton's second law. The viscoelastic model is taken to be the Kelvin-Voigt model. In the first section, the static deflection is obtained using the Galerkin method. Exact linear symmetric mode shape of a straight beam and its deflection function under constant transverse load are used as admissible functions. So, an analytical expression that describes the static deflection at all points is obtained. Comparing the result with previous research show that using deflection function as admissible function decreases the computation errors and previous calculations volume. In the second section, the response of a microbeam resonator system under primary and secondary resonance excitation has been obtained by analytical multiple scale perturbation method combined with the Galerkin method. It is shown, that a small amount of viscoelastic damping has an important effect and causes to decrease the maximum amplitude of response, and to shift the resonance frequency. Also, it shown, that an increase of the DC voltage, ratio of the air gap to the microbeam thickness, tensile axial load, would increase the effect of viscoelastic damping, and an increase of the compressive axial load would decrease the effect of viscoelastic damping.
Ghayesh, M.H.,Khadem, S.E. Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.27 No.1
The main source of transverse vibration of a conveyor belt is frictional contact between pulley and belt. Also, environmental characteristics such as natural dampers and springs affect natural frequencies, stability and bifurcation points of system. These phenomena can be modeled by a small velocity fluctuation about mean velocity. Also, viscoelastic foundation can be modeled as the dampers and springs with continuous characteristics. In this study, non-linear vibration of a conveyor belt supported partially by a distributed viscoelastic foundation is investigated. Perturbation method is applied to obtain a closed form analytic solutions. Finally, numerical simulations are presented to show stiffness, damping coefficient, foundation length, non-linearity and mean velocity effects on location of bifurcation points, natural frequencies and stability of solutions.
Resonantly excited ZnO nanowires for fabrication of high sensitivity gas sensor
Y. Abdi,S.M. Jebreiil Khadem,P. Afzali 한국물리학회 2014 Current Applied Physics Vol.14 No.3
A novel approach for gas sensing based on mechanical resonance of ZnO nanowires is reported. For this purpose, ZnO nanowires were grown between comb-like electrodes using a novel oxygen plasma treatment approach. Then gas measurements were carried out at different agitating frequency. Results show an improvement in gas sensitivity of resonantly excited ZnO nanowires. Our results open up a promising approach to fabricate high sensitivity gas sensor. Also we have introduced an alternative frequency modulation gas detection method here.