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    Size dependence and effect of potential parameters on properties of nano-cavities in liquid xenon using molecular dynamics simulation

    , Article Chemical Physics ; Volume 381, Issue 1-3 , March , 2011 , Pages 44-48 ; 03010104 (ISSN) Akbarzadeh, H ; Abroshan, H ; Taherkhani, F ; Izanloo, C ; Parsafar, G. A ; Sharif University of Technology
    We have investigated the size dependence of a nano-cavity properties produced in a Xe fluid using molecular dynamics simulations. We have created a nano-cavity of different sizes at 170 and 200 K (cavities diameters are within 1-10 nm). Liquid pressure, vapor pressure and surface tension of the nano-cavity for some given values of diameter are calculated. Within 1-10 nm cavity diameter, we have observed two opposite behavior for dependency of surface tension on the cavity diameter: for the range of 1-5 nm, it increases with the diameter, while, for the range of 5-10 nm remains constant. Also, the value of liquid pressure becomes less negative, when the size of cavity increases. Vapor... 

    Calculation of effective pair potential via the volumetric data

    , Article Phase Transitions ; Vol. 87, issue. 1 , 2014 , pp. 38-58 ; ISSN: 01411594 Namdari, F ; Parsafar, G ; Sharif University of Technology
    The concept of effective pair potential (EPP), in which medium effects and contribution of long-range interactions are added to near-neighbor pair interactions, is a useful tool to derive and calculate the thermodynamic quantities. It has been shown that the extended Lennard-Jones (12, 6, 3) potential is an accurate EPP for many systems. However, the parameters of this EPP are not known for any systems. We introduce a new approach to use experimental pvT data of a fluid to calculate its EPP parameters. Such calculation has been carried out for some fluids at some temperatures. Unlike the isolated pair potential, it has been shown that the parameters significantly vary with temperature. We... 

    Energy-landscape networks of spin glasses

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 77, Issue 3 , 2008 ; 15393755 (ISSN) Seyed Allaei, H ; Seyed Allaei, H ; Ejtehadi, M. R ; Sharif University of Technology
    We have studied the topology of the energy landscape of a spin-glass model and the effect of frustration on it by looking at the connectivity and disconnectivity graphs of the inherent structure. The connectivity network shows the adjacency of energy minima whereas the disconnectivity network tells us about the heights of the energy barriers. Both graphs are constructed by the exact enumeration of a two-dimensional square lattice of a frustrated spin glass with nearest-neighbor interactions up to the size of 27 spins. The enumeration of the energy-landscape minima as well as the analytical mean-field approximation show that these minima have a Gaussian distribution, and the connectivity... 

    Calculation of thermodynamic properties of simple fluids using a new derived pair correlation function

    , Article Fluid Phase Equilibria ; Volume 254, Issue 1-2 , 2007 , Pages 138-143 ; 03783812 (ISSN) Khanpour, M ; Parsafar, G. A ; Najafi, B ; Sharif University of Technology
    Based on a new derived radial distribution function (RDF) for potentials with a hard-core we have presented in this paper a method to apply the derived RDF for calculating thermodynamic properties of real fluids up to moderate densities. In order to use the derived RDF for real fluids, one of the potential parameters is chosen in such a way that the RDF behaves more like that for a real fluid. Hence we have been able to calculate all thermodynamic properties of a simple fluid analytically. We have then applied our procedure to a Lennard-Jones fluid and compared the results with simulation data. The agreement is good up to moderate densities, i.e. ρ* ≤ 0.6, which lies in the liquid range of... 

    Analytical first derivatives of the RE-squared interaction potential

    , Article Journal of Computational Physics ; Volume 219, Issue 2 , 2006 , Pages 770-779 ; 00219991 (ISSN) Babadi, M ; Ejtehadi, M. R ; Everaers, R ; Sharif University of Technology
    Academic Press Inc  2006
    We derive exact expressions for the forces and torques between biaxial molecules interacting via the RE-squared potential, a recent variant of the Gay-Berne potential. Moreover, efficient routines have been provided for rigid body MD simulations, resulting in 1.6 times speedup compared to the two-point finite difference approach. It has also been shown that the time cost of a MD simulation will be almost equal to a similar MC simulation, making use of the provided routines. © 2006 Elsevier Inc. All rights reserved  

    Influence of quantum effect on deviation from linear isotherm regularity

    , Article Scientia Iranica ; Volume 19, Issue 3 , June , 2012 , Pages 555-560 ; 10263098 (ISSN) Safdari, F ; Parsafar, G. A ; Sharif University of Technology
    A general regularity was found based on an effective pair potential of Lennard-Jones LJ (12, 6), for both dense, nonmetallic and nonionic fluids and solids according to which (Z-1) v2 linearly varies with respect to ρ2 for each isotherm, and this equation of state (EoS I) is known as LIR. However, despite the fact that Ne is a simple spherical species, unexpectedly, its solid and liquid phases both show a significant deviation from EoS I. In this work, we have investigated the accuracy of the EoS I for other systems, including quantum light molecules, such as D 2, H 2 and He, in both fluid and solid states at different temperatures. Like Ne, we have noticed that these systems do not well... 

    Toward an equation of state for water inside carbon nanotubes

    , Article Journal of Physical Chemistry B ; Volume 116, Issue 16 , April , 2012 , Pages 4943-4951 ; 15206106 (ISSN) Sadeghi, M ; Parsafar, G. A ; Sharif University of Technology
    American Chemical Society  2012
    Water inside carbon nanotubes as an example of nanoconfined water has gained noticeable attention, in both theoretical and applied aspects. Molecular simulation has played a major role in the studies in this field. Yet, there is a need for systematic study of simulation results and compilation of scientifically reliable predictive relations. Here we present Monte Carlo simulations of water inside carbon nanotubes with different radii. An equation of state which was derived on the basis of the extended Lennard-Jones (12,6,3) as the effective pair potential is chosen for the system of water inside the carbon nanotubes. The equation of state is modified to take the effects of anisotropic... 

    Complex self-propelled rings: A minimal model for cell motility

    , Article Soft Matter ; Volume 13, Issue 35 , 2017 , Pages 5865-5876 ; 1744683X (ISSN) Abaurrea Velasco, C ; Dehghani Ghahnaviyeh, S ; Nejat Pishkenari, H ; Auth, T ; Gompper, G ; Sharif University of Technology
    Royal Society of Chemistry  2017
    Collective behavior of active matter is observed for self-propelled particles, such as vibrated disks and active Brownian particles, as well as for cytoskeletal filaments in motile cells. Here, a system of quasi two-dimensional penetrable self-propelled rods inside rigid rings is used to construct a complex self-propelled particle. The rods interact sterically with each other and with a stationary or mobile ring via a separation-shifted Lennard-Jones potential. They either have a sliding attachment to the inside of the ring at one of their ends, or can move freely within the ring confinement. We study the inner structure and dynamics of the mobile self-propelled rings. We find that these... 

    Solvation free energy and solubility of acetaminophen and ibuprofen in supercritical carbon dioxide: Impact of the solvent model

    , Article Journal of Supercritical Fluids ; Volume 109 , 2016 , Pages 166-176 ; 08968446 (ISSN) Noroozi, J ; Ghotbi, C ; Jahanbin Sardroodi, J ; Karimi Sabet, J ; Robert, M. A ; Sharif University of Technology
    Elsevier  2016
    Classical molecular dynamics simulations are used to compute the solvation free energy of two pharmaceutical solids, namely ibuprofen and acetaminophen in carbon dioxide (CO2), over the density range of interest in supercritical processes. In order to examine the influence of the solvent model on the resulting free energies, three popular CO2 models (Zhang, EPM2, and TraPPE) are studied. Relatively large discrepancies for the solvation free energy exist between these CO2 models, suggesting that the former is sensitive to the different balances between dispersive and electrostatic forces used in these models. In particular, for the solvation of the highly polar (dipole moment of ∼5.2 Debye)... 

    Nanoscopic spontaneous motion of liquid trains: Nonequilibrium molecular dynamics simulation

    , Article Journal of Chemical Physics ; Volume 132, Issue 2 , 2010 ; 00219606 (ISSN) Bahrami, A. H ; Jalali, M. A ; Sharif University of Technology
    Macroscale experiments show that a train of two immiscible liquid drops, a bislug, can spontaneously move in a capillary tube because of surface tension asymmetries. We use molecular dynamics simulation of Lennard-Jones fluids to demonstrate this phenomenon for NVT ensembles in submicron tubes. We deliberately tune the strength of intermolecular forces and control the velocity of bislug in different wetting and viscosity conditions. We compute the velocity profile of particles across the tube and explain the origin of deviations from the classical parabolae. We show that the self-generated molecular flow resembles the Poiseuille law when the ratio of the tube radius to its length is less... 

    Bidirectional water transport through non-straight carbon nanotubes

    , Article Journal of Molecular Liquids ; Volume 276 , 2019 , Pages 39-46 ; 01677322 (ISSN) Kargar, S ; Moosavi, A ; Sharif University of Technology
    Elsevier B.V  2019
    Natural nanochannels and those used for applied purposes are often several nanometers in diameter and have lengths up to micrometer scales. Since normally no pressure gradient, mechanical force or electrical field is exerted on fluids in these situations, the fluid flow within them is not single-file and can be bidirectional. For this reason, studying the behavior of bidirectional flows in the channels is of paramount importance. In this study, a comprehensive investigation on the straight and non-straight bidirectional water transfer through carbon nanotubes is conducted via extensive molecular dynamics simulations. The results indicate that by changing the length, the diameter and the... 

    Designing an intelligent controller for a molecular valve

    , Article 2008 Proceedings of the ASME - 2nd International Conference on Integration and Commercialization of Micro and Nanosystems, MicroNano 2008, 3 June 2008 through 5 June 2008, Kowloon ; 2008 , Pages 195-201 ; 0791842940 (ISBN); 9780791842942 (ISBN) Momeni, K ; Alasty, A ; Sharif University of Technology
    Too much effort has been done for manipulating individual atoms, using nano-manipulators and Scanning Tunneling Microscopes (STM). On the other hand, characterization and manipulation of nano-flows is of great concern. In the current work a molecular valve has been considered, which is made up of six atoms placed on the circumstance of a circle. A fuzzy controller has been designed for controlling the diameter of this molecular valve. The designed fuzzy controller used singleton fuzzifier, Mamdani inference engine, center average defuzzifier and exponential membership functions. A model based on the classical Molecular Dynamics (MD) is used for modeling the nano-system and passing the states... 

    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
    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... 

    Study of microstructural growth under cyclic martensite phase transition in shape memory alloys; A molecular dynamics approach

    , Article Journal of Intelligent Material Systems and Structures ; 2021 ; 1045389X (ISSN) Moravej, S. A ; Taghibakhshi, A ; Nejat Pishkenari, H ; Arghavani, J ; Sharif University of Technology
    SAGE Publications Ltd  2021
    Shape memory alloys are referred to as a group of alloys that can retrieve the permanent deformation and strain applied to them and eventually return to their original form. So far, various studies have been done to determine the behavior of these alloys under cyclic loading. Most of the studies have mainly been conducted by using the foundations of Continuum Mechanics in order to examine the properties of memory alloys. In this study, instead of using the Continuum Mechanics, a Molecular Dynamics simulation method using Lennard-Jones potential is utilized. The changes in the behavior and properties of memory alloy under cyclic loading are being examined. First, the functional form... 

    The effects of geometrical parameters on force distributions and mechanics of carbon nanotubes: A critical study

    , Article Communications in Nonlinear Science and Numerical Simulation ; Volume 14, Issue 12 , 2009 , Pages 4246-4263 ; 10075704 (ISSN) Ansari, R ; Motevalli, B ; Sharif University of Technology
    In this paper, using the continuum approximation together with Lennard-Jones potential, a new semi-analytical expression is given to evaluate the van der Waals interaction between two single-walled carbon nanotubes. Based on this expression, two new formulations are also proposed to model multi-walled carbon nanotubes. In the first one, the interactions between each pair of shells from the inner and outer tubes are summed up over all of the pairs, whereas in the second formulation, a set of correction factors are applied to convert the results of double-walled carbon nanotubes to the correlated multi-walled ones. With respect to the present formulations, extensive studies on the variations... 

    Study the effect of viscoelastic matrix model on the stability of CNT/polymer composites by multiscale modeling

    , Article Polymer Composites ; Volume 30, Issue 11 , 2009 , Pages 1545-1551 ; 02728397 (ISSN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology
    In this article, a Molecular Structural Mechanics/Finite Element (MSM/FE) multiscale modeling of carbon nanotube/polymer composites with viscoelastic (VE) polymer matrix is introduced. The nanotube is modeled at the atomistic scale using structural molecular mechanics. The matrix deformation is analyzed by nonlinear finite element method considering VE behavior. The nanotube and matrix are assumed to be bonded by van der Waals interactions based on the Lennard-Jones potential at the interface. Using the MSM/FE multiscale model, we investigate the effect of carbon nanotube (CNT) on the improvement of mechanical stability of the nanocomposite. Also, the buckling behavior of these... 

    An accurate equation of state for fluids and solids

    , Article Journal of Physical Chemistry B ; Volume 113, Issue 35 , 2009 , Pages 11977-11987 ; 15206106 (ISSN) Parsafar, G. A ; Spohr, H. V ; Patey, G. N ; Sharif University of Technology
    American Chemical Society  2009
    A simple functional form for a general equation of state based on an effective near-neighbor pair interaction of an extended Lennard-Jones (12,6,3) type is given and tested against experimental data for a wide variety of fluids and solids. Computer simulation results for ionic liquids are used for further evaluation. For fluids, there appears to be no upper density limitation on the equation of state. The lower density limit for isotherms near the critical temperature is the critical density. The equation of state gives a good description of all types of fluids, nonpolar (including long-chain hydrocarbons), polar, hydrogen-bonded, and metallic, at temperatures ranging from the triple point... 

    Simulation of heat transfer in nanoscale flow using molecular dynamics

    , Article ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels Collocated with 3rd Joint US-European Fluids Engineering Summer Meeting, ICNMM2010, 1 August 2010 through 5 August 2010, Montreal, QC ; Issue PARTS A AND B , 2010 , Pages 1563-1568 ; 9780791854501 (ISBN) Darbandi, M ; Abbasi, H. R ; Sabouri, M ; Khaledi Alidusti, R ; Sharif University of Technology
    We investigate heat transfer between parallel plates separated by liquid argon using two-dimensional molecular dynamics (MD) simulations incorporating with 6-12 Lennard-Jones potential between molecule pairs. In molecular dynamics simulation of nanoscale flows through nanochannels, it is customary to fix the wall molecules. However, this approach cannot suitably model the heat transfer between the fluid molecules and wall molecules. Alternatively, we use thermal walls constructed from the oscillating molecules, which are connected to their original positions using linear spring forces. This approach is much more effective than the one which uses a fixed lattice wall modeling to simulate the... 

    Investigation of the interphase effects on the mechanical behavior of carbon nanotube polymer composites by multiscale modeling

    , Article Journal of Applied Polymer Science ; Volume 117, Issue 1 , March , 2010 , Pages 361-367 ; 00218995 (ISSN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology
    In this article, a multiscale modeling procedure is implemented to study the effect of interphase on the Young's modulus of CNT/polymer composites. For this purpose, a three-phase RVE is introduced which consists of three components, i.e., a carbon nanotube, an interphase layer, and an outer polymer matrix. The nanotube is modeled at the atomistic scale using molecular structural mechanics. Moreover, three-dimensional elements are employed to model the interphase layer and polymer matrix. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions based on the Lennard-Jones potential at the interface. Using this Molecular Structural Mechanics/Finite Element... 

    Investigating the effect of carbon nanotube defects on the column and shell buckling of carbon nanotube-polymer composites using multiscale modeling

    , Article International Journal for Multiscale Computational Engineering ; Volume 7, Issue 5 , 2009 , Pages 431-444 ; 15431649 (ISSN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology
    Carbon nanotube (CNT)-reinforced polymer composites have attracted great attention due to their exceptionally high strength. Their high strength can be affected by the presence of defects in the nanotubes used as reinforcements in practical nanocomposites. In this article, a new three-phase molecular structural mechanics/finite element (MSM/FE) multiscale model is used to study the effect of CNT vacancy defects on the stability of single-wall (SW) CNT-polymer composites. The nanotube is modeled at the atomistic scale using MSM, whereas the interphase layer and polymer matrix are analyzed by the FE method. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions...