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    Chaos control in Bonhoeffer-van der pol system using fuzzy estimation

    , Article Proceedings of the 7th Biennial Conference on Engineering Systems Design and Analysis - 2004, Manchester, 19 July 2004 through 22 July 2004 ; Volume 1 , 2004 , Pages 885-894 ; 0791841731 (ISBN); 9780791841730 (ISBN) Alasty, A ; Salarieh, H ; Sharif University of Technology
    American Society of Mechanical Engineers  2004
    Abstract
    This paper illustrates the control of chaos using a fuzzy estimating system based on batch training and recursive least square methods for a continuous time dynamic system. The fuzzy estimator system is trained on both Ott-Geobogi-Yorke (OGY) control algorithm and Pyragas's delayed feedback control algorithm. The system, considered for this study, is a Bonhoeffer-van der Pol (BVP) oscillator. It is found that the implemented fuzzy control system constructed on OGY algorithm results in smaller control transient response than that of the OGY control algorithm itself. The transient response of Pyragas fuzzy control does not show a significant improvement in compare to the Pyragas control... 

    Effects of casimir and van der waals forces on the pull-in instability of the nonlinear micro and nano-bridge gyroscopes

    , Article International Journal of Structural Stability and Dynamics ; Vol. 14, issue. 2 , 2014 ; ISSN: 02194554 Mojahedi, M ; Ahmadian, M. T ; Firoozbakhsh, K ; Sharif University of Technology
    Abstract
    The influence of Casimir and van der Waals forces on the instability of vibratory micro and nano-bridge gyroscopes with proof mass attached to its midpoint is studied. The gyroscope subjected to the base rotation, Casimir and van der Waals attractions is actuated and detected by electrostatic methods. The system has two coupled bending motions actuated by the electrostatic and Coriolis forces. First a system of nonlinear equations for the flexural-flexural deflection of beam gyroscopes is derived using the extended Hamilton's principle. In modeling, the nonlinearities due to mid-plane stretching, electrostatic forces, including fringing field, Casimir and van der Waals attractions, are... 

    Nanoscale modeling of an embedded multi-shell fullerene and its application to vibrational analysis

    , Article International Journal of Engineering Science ; Volume 44, Issue 17 , 2006 , Pages 1156-1163 ; 00207225 (ISSN) Behfar, K ; Naghdabadi, R ; Sharif University of Technology
    2006
    Abstract
    In this paper, nanoscale modeling of a multi-shell fullerene embedded in an elastic medium and its application to vibrational analysis is investigated. The spherical layers of the multi-shell fullerene are concentrically nested, with carbon-carbon van der Waals interactions between them. Also, the whole multi-shell fullerene is influenced by polymer-carbon van der Waals forces from the surrounding elastic medium. The elasticity generated by the carbon-carbon bonds is assumed to be distributed isotropically over the fullerene surfaces. Following derivation of explicit equations for the motion of the multi-shell fullerene, vibrational behavior of a double-shell fullerene is analyzed and... 

    Acquisition of high precision images for non-contact atomic force microscopy via direct identification of sample height

    , Article 2005 ASME International Mechanical Engineering Congress and Exposition, IMECE 2005, Orlando, FL, 5 November 2005 through 11 November 2005 ; Volume 74 DSC, Issue 2 PART B , 2005 , Pages 1335-1342 ; 0791842169 (ISBN); 9780791842164 (ISBN) Pishkenari, H. N ; Jalili, N ; Meghdari, A ; Sharif University of Technology
    2005
    Abstract
    Atomic force microscopes (AFM) can image and manipulate sample properties at the atomic scale. The non-contact mode of AFM offers unique advantages over other contemporary scanning probe techniques, especially when utilized for reliable measurements of soft samples (e.g., biological species). The distance between cantilever tip and sample surface is a time varying parameter even for a fixed sample height, and hence, difficult to identify. A remedy to this problem is to directly identify the sample height in order to generate high precision, atomic-resolution images. For this, the microcantilever is modeled by a single mode approximation and the interaction between the sample and cantilever... 

    Van der Waals energy surface of a carbon nanotube sheet

    , Article Solid State Communications ; Volume 152, Issue 3 , February , 2012 , Pages 225-230 ; 00381098 (ISSN) Motahari, S ; Shayeganfar, F ; Neek Amal, M ; Sharif University of Technology
    Abstract
    The van der Walls interaction between a carbon nanotube sheet (CNTS) and a rare gas atom, is studied using both atomistic and continuum approaches. We present analytical expressions for the van der Waals energy of continuous nanotubes interacting with a rare gas atom. It is found that the continuum approach does not properly treat the effect of atomistic configurations on the energy surfaces. The energy barriers are small as compared to the thermal energy, which implies the free motion above the CNTS in heights about one nanometer. In contrast to the energy surface of a graphene sheet, the honeycomb lattice structure in the energy surface of a CNTS is imperceivable. Defects alter the energy... 

    Managing distributed energy resources (DERS) through virtual power plant technology (VPP): a stochastic information-gap decision theory (IGDT) approach

    , Article Iranian Journal of Science and Technology - Transactions of Electrical Engineering ; Volume 44, Issue 1 , 2020 , Pages 279-291 Alahyari, A ; Ehsan, M ; Moghimi, M ; Sharif University of Technology
    Springer  2020
    Abstract
    As the number of distributed energy resources (DERs) increases, so would their influences on the power systems. Toward managing the intermittent nature of DERs, and providing market participation capability, the concept of virtual power plant (VPP) has been developed in the smart grid era. This paper proposes a novel offering strategy method for a VPP consisting of wind power generation along with storage capacity and flexible demand. In the proposed method, two different sources of uncertainty are addressed: stochastic method, applied in dealing with market price uncertainty, and information-gap decision theory (IGDT), incorporated in the offering model counting for wind power production... 

    Tunable gain SnS2/InSe Van der waals heterostructure photodetector

    , Article Micromachines ; Volume 13, Issue 12 , 2022 ; 2072666X (ISSN) Hosseini, S ; Iraji zad, A ; Mahdavi, S. M ; Esfandiar, A ; Sharif University of Technology
    MDPI  2022
    Abstract
    Due to the favorable properties of two-dimensional materials such as SnS2, with an energy gap in the visible light spectrum, and InSe, with high electron mobility, the combination of them can create a novel platform for electronic and optical devices. Herein, we study a tunable gain SnS2/InSe Van der Waals heterostructure photodetector. SnS2 crystals were synthesized by chemical vapor transport method and characterized using X-ray diffraction and Raman spectroscopy. The exfoliated SnS2 and InSe layers were transferred on the substrate. This photodetector presents photoresponsivity from 14 mA/W up to 740 mA/W and detectivity from 2.2 × 108 Jones up to 3.35 × 109 Jones by gate modulation from... 

    Static feedback versus fractionality of the electrical elements in the Van der Pol circuit

    , Article Nonlinear Dynamics ; Volume 72, Issue 1-2 , 2013 , Pages 365-375 ; 0924090X (ISSN) Tavakoli Kakhki, M ; Tavazoei, M. S ; Sharif University of Technology
    2013
    Abstract
    In this paper, it is shown that by benefiting from a static feedback control signal it is possible to reduce the effect of fractionality of the electrical capacitors on the amplitude of the oscillations produced by a Van der Pol circuit. The averaging method is used in this paper for the behavior analysis of the approximated responses of the under study circuits. Numerical simulation results are presented to confirm the effectiveness of the proposed control technique  

    An analytical approach to modeling static behavior of torsional nano-/micro-actuators under effect of van der Waals force

    , Article Japanese Journal of Applied Physics ; Volume 51, Issue 3 PART 1 , 2012 ; 00214922 (ISSN) Moeenfard, H ; Darvishian, A ; Ahmaidan, M. T ; Zohoor, H ; Sharif University of Technology
    Abstract
    In this research, the static behavior of torsional nano-/micro-actuators under van der Waals (vdW) force is studied. First, the equilibrium equation governing the static behavior of torsional nano-/micro-actuators under vdW force is obtained. Then the energy method is utilized to investigate the statical stability of nano-/micro-actuator equilibrium points and a useful equation is suggested for the successful and stable design of nano-/micro-actuators under vdW force. Then, the equilibrium angle of nano-/micro-actuators is calculated both numerically and analytically using the homotopy perturbation method (HPM). It is observed that, with increasing instability number, defined in this paper,... 

    Prediction of Henry's constant in polymer solutions using PCOR equation of state coupled with an activity coefficient model

    , Article Chinese Journal of Chemical Engineering ; Volume 23, Issue 3 , 2015 , Pages 528-535 ; 10049541 (ISSN) Tourani, S ; Behvandi, A ; Khorasheh, F ; Sharif University of Technology
    Abstract
    In this paper, the polymer chain of rotator (PCOR) equation of state (EOS) was used together with an EOS/GE mixing rule (MHV1) and the Wilson's equation as an excess-Gibbs-energy model in the proposed approach to extend the capability and improve the accuracy of the PCOR EOS for predicting the Henry's constant of solutions containing polymers. The results of the proposed method compared with two equation of state (van der Waals and GC-Flory) and three activity coefficient models (UNIFAC, UNIFAC-FV and Entropic-FV) indicated that the PCOR EOS/Wilson's equation provided more accurate results. The interaction parameters of Wilson's equation were fitted with Henry's constant experimental data... 

    Influence of intermolecular forces on dynamic pull-in instability of micro/nano bridges

    , Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010 ; Volume 5 , 2010 , Pages 655-662 ; 9780791849194 (ISBN) Moghimi Zand, M ; Ahmadian, M. T ; Sharif University of Technology
    Abstract
    In this study, influences of intermolecular forces on dynamic pull-in instability of electrostatically actuated beams are investigated. Effects of midplane stretching, electrostatic actuation, fringing fields and intermolecular forces are considered. The boundary conditions of the beams are clamped-free and clamped-clamped. A finite element model is developed to discretize the governing equations and Newmark time discretization is then employed to solve the discretized equations. The results indicate that by increasing the Casimir and van der Waals effects, the effect of inertia on pull-in values considerably increases  

    Diffusive motion of C60 on a graphene sheet

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 82, Issue 5 , November , 2010 ; 15393755 (ISSN) Neek Amal, M ; Abedpour, N ; Rasuli, S. N ; Naji, A ; Ejtehadi, M. R ; Sharif University of Technology
    2010
    Abstract
    The motion of a C60 molecule over a graphene sheet at finite temperature is investigated both theoretically and computationally. We show that a graphene sheet generates a van der Waals laterally periodic potential, which directly influences the motion of external objects in its proximity. The translational motion of a C60 molecule near a graphene sheet is found to be diffusive in the lateral directions, while in the perpendicular direction, the motion may be described as diffusion in an effective harmonic potential which is determined from the distribution function of the position of the C60 molecule. We also examine the rotational diffusion of C 60 and show that its motion over the graphene... 

    Instability of nanocantilever arrays in electrostatic and van der waals interactions

    , Article Journal of Physics D: Applied Physics ; Volume 42, Issue 22 , 2009 ; 00223727 (ISSN) Ramezani, A ; Alasty, A ; Sharif University of Technology
    2009
    Abstract
    The structural instability of an array of cantilevers, each of which interacts with two neighbouring beams through electrostatic and van der Waals forces, is studied. Distributed and lumped parameter modelling of the array result in a set of coupled nonlinear boundary value problems and a set of coupled nonlinear equations, respectively. These coupled nonlinear systems are solved numerically for different numbers of beams in the array to obtain the pull-in parameters. The pull-in parameters converge to constant values with an increase in the number of beams in the array. These constants, which are important in the design of cantilever arrays, are compared for the distributed and lumped... 

    Investigation the stability of SWCNT-polymer composites in the presence of CNT geometrical defects using multiscale modeling

    , Article 4th International Conference on Multiscale Materials Modeling, MMM 2008, 27 October 2008 through 31 October 2008 ; 2008 , Pages 163-166 ; 9780615247816 (ISBN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology
    Department of Scientific Computing, Florida State University  2008
    Abstract
    CNT-reinforced polymer composites have attracted attention due to their exceptional high strength. The high strength can be affected by the presence of defects in the nanotubes used as reinforcements in the practical nanocomposites. In this paper, a Molecular Structural Mechanics / Finite Element (MSM/FE) multiscale modeling is used to study the effect of carbon nanotube geometrical defects on the stability of SWCNT-polymer composites. Here, two types of representative volume elements (RVEs) for these nanocomposites are considered with perfect and defected CNT. These RVEs have the same dimensions. The nanotube is modeled at the atomistic scale using molecular structural mechanics whereas the... 

    Mechanical hydrolysis imparts self-destruction of water molecules under steric confinement

    , Article Physical Chemistry Chemical Physics ; Volume 23, Issue 10 , 2021 , Pages 5999-6008 ; 14639076 (ISSN) Hosseini, E ; Zakertabrizi, M ; Habibnejad Korayem, A ; Carbone, P ; Esfandiar, A ; Shahsavari, R ; Sharif University of Technology
    Royal Society of Chemistry  2021
    Abstract
    Decoding behavioral aspects associated with the water molecules in confined spaces such as an interlayer space of two-dimensional nanosheets is key for the fundamental understanding of water-matter interactions and identifying unexpected phenomena of water molecules in chemistry and physics. Although numerous studies have been conducted on the behavior of water molecules in confined spaces, their reach stops at the properties of the planar ice-like formation, where van der Waals interactions are the predominant interactions and many questions on the confined space such as the possibility of electron exchange and excitation state remain unsettled. We used density functional theory and... 

    Analytical modeling of static behavior of electrostatically actuated nano/micromirrors considering van der Waals forces

    , Article Acta Mechanica Sinica/Lixue Xuebao ; Volume 28, Issue 3 , June , 2012 , Pages 729-736 ; 05677718 (ISSN) Moeenfard, H ; Ahmadian, M. T ; Sharif University of Technology
    2012
    Abstract
    In this paper, the effect of van der Waals (vdW) force on the pull-in behavior of electrostatically actuated nano/micromirrors is investigated. First, the minimum potential energy principle is utilized to find the equation governing the static behavior of nano/micromirror under electrostatic and vdW forces. Then, the stability of static equilibrium points is analyzed using the energy method. It is found that when there exist two equilibrium points, the smaller one is stable and the larger one is unstable. The effects of different design parameters on the mirror's pull-in angle and pull-in voltage are studied and it is found that vdW force can considerably reduce the stability limit of the... 

    Approximation behavior of Van der Pol equation: Large and small nonlinearity parameter

    , Article IMECS 2011 - International MultiConference of Engineers and Computer Scientists 2011, 16 March 2011 through 18 March 2011 ; Volume 2 , March , 2011 , Pages 1539-1544 ; 9789881925121 (ISBN) Azarkhalili, B ; Moghadas, P ; Rasouli, M ; Sharif University of Technology
    2011
    Abstract
    The labels mathematician, engineer, and physicist have all been used in reference to Balthazar van der Pol. The van der Pol oscillator, which we study in this paper, is a model developed by him to describe the behavior of nonlinear vacuum tube circuits in the relatively early days of the development of electronics technology. Our study in this paper will be based entirely on numerical solutions. The rigorous foundations for the analysis (e.g., the proof that the equation has a limit cycle solution which is a global attractor) date back to the work of Lienard in 1928, with later more general analysis by Levinson and others  

    Classical and recent free-volume models for polymer solutions: a comparative evaluation

    , Article Fluid Phase Equilibria ; Volume 257, Issue 1 , 2007 , Pages 63-69 ; 03783812 (ISSN) Radfarnia, H. R ; Kontogeorgis, G.M ; Ghotbi, Cyrus ; Taghikhani, Vahid ; Sharif University of Technology
    2007
    Abstract
    In this work, two "classical" (UNIFAC-FV, Entropic-FV) and two "recent" free-volume (FV) models (Kannan-FV, Freed-FV) are comparatively evaluated for polymer-solvent vapor-liquid equilibria including both aqueous and non-aqueous solutions. Moreover, some further developments are presented here to improve the performance of a recent model, the so-called Freed-FV. First, we propose a modification of the Freed-FV model accounting for the anomalous free-volume behavior of aqueous systems (unlike the other solvents, water has a lower free-volume percentage than polymers). The results predicted by the modified Freed-FV model for athermal and non-athermal polymer systems are compared to other... 

    Torsional buckling of carbon nanopeapods

    , Article Carbon ; Volume 45, Issue 5 , 2007 , Pages 952-957 ; 00086223 (ISSN) Najafi Sohi, A ; Naghdabadi, R ; Sharif University of Technology
    2007
    Abstract
    Torsional buckling of carbon nanopeapods (carbon nanotubes filled with fullerenes) is studied using a continuum-based multi-layered shell model. The model takes into account non-bonded van der Waals interactions between nested fullerenes and the innermost layer of host nanotube. For nanopeapods with linearly arranged nested fullerenes, equivalent pressure distribution is proposed to model these interactions. Deriving explicit equations governing the torsional stability, it is concluded that the critical torsional load of a carbon nanopeapod is less than that of a carbon nanotube under otherwise identical geometric and mechanical conditions. Performing numerical calculations, it is also shown... 

    Bending stiffness of a double-layered graphene sheet using a geometrically-based analytical approach

    , Article 4th ASME Integrated Nanosystems Conference: Design, Synthesis, and Applications, Berkeley, CA, 14 September 2005 through 16 September 2005 ; 2005 , Pages 85-86 ; 0791842088 (ISBN); 9780791842089 (ISBN) Behfar, K ; Naghdabadi, R ; Sharif University of Technology
    American Society of Mechanical Engineers  2005
    Abstract
    In this article, the bending stiffness of a double-layered graphene sheet is investigated using a geometrically-based analytical approach. The analysis is based on the van der Waals interactions of atoms belonging to two neighboring sheets. The inter-atomic spacing between the adjacent layers is geometrically determined when the sheet is applied by a couple of moments in the opposite sides. The bending potential energy is obtained by summing up the potentials at discrete hexagons over the length and width of the sheet. It is observed that the bending stiffness of a double-layered graphene sheet does not depend on the length of the sheet and be a material property for the associated sheet....