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Total 25 records

    Fracture analysis of monolayer graphene sheets with double vacancy defects via MD simulation

    , Article Solid State Communications ; Volume 151, Issue 17 , 2011 , Pages 1141-1146 ; 00381098 (ISSN) Ansari, R ; Motevalli, B ; Montazeri, A ; Ajori, S ; Sharif University of Technology
    Abstract
    Carbon nanostructures such as carbon nanotubes (CNTs) and graphene sheets have attracted great attention due to their exceptionally high strength and elastic strain. These extraordinary mechanical properties, however, can be affected by the presence of defects in their structures. When a material contains multiple defects, it is expected that the stress concentration of them superposes if the separation distances of the defects are low, which causes a more reduction of the strength. On the other hand, it is believed that if the defects are far enough such that their affected areas are distinct, their behavior is similar to a material with single defect. In this article, molecular dynamics... 

    Investigation of the gas barrier properties of PP/ciay nanocomposite films with EVA as a compatibiliser prepared by the melt intercalation method

    , Article Polymer - Plastics Technology and Engineering ; Volume 49, Issue 10 , 2010 , Pages 991-995 ; 03602559 (ISSN) Shafiee, M ; Ahmad Ramazani, S. A ; Danaei, M ; Sharif University of Technology
    2010
    Abstract
    In this research, polypropylene (PP) nanocomposite films were prepared by melt intercalation method and their properties have been evaluated. To facilitate the formation of either intercalated or exfoliated nanocomposites, ethylene vinyl acetate copolymer (EVA) was used as a compatibiliser. Morphology of composites was determined by X-ray Diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM analyses confirmed that increasing of EVA content leads to achievement of intercalated nanocomposites. Furthermore, differential scanning calorimetry (DSC) measurement indicated a decrease in crystallinity, melting point and crystallization temperature. Also, permeability tests showed... 

    Micro resonator nonlinear dynamics considering intrinsic properties

    , Article Scientia Iranica ; Volume 16, Issue 2 B , 2009 , Pages 121-129 ; 10263098 (ISSN) Sayyaadi, H ; Tadayon, M. A ; Eftekharian, A. A ; Sharif University of Technology
    2009
    Abstract
    One of the most important phenomena to affect the motion behaviour of Micro Resonators is their thermal dependency. This has recently received the attention of researchers widely. A thermal phenomenon has two main effects, the first is damping, due to internal friction, and the second is softening, due to Young's modulus-temperature relationship. In this research work, some theoretical and experimental reported results are used to make a proper model, including thermal phenomena. Two Lorentzian functions are used to describe the restoring and damping forces caused by thermal phenomena. In order to emphasize the thermal effects, a nonlinear model of the MEMS, considering capacitor... 

    Nanomechanical properties of MscL α helices: A steered molecular dynamics study

    , Article Channels ; Volume 11, Issue 3 , 2017 , Pages 209-223 ; 19336950 (ISSN) Bavi, N ; Bavi, O ; Vossoughi, M ; Naghdabadi, R ; Hill, A. P ; Martinac, B ; Jamali, Y ; Sharif University of Technology
    Taylor and Francis Inc  2017
    Abstract
    Gating of mechanosensitive (MS) channels is driven by a hierarchical cascade of movements and deformations of transmembrane helices in response to bilayer tension. Determining the intrinsic mechanical properties of the individual transmembrane helices is therefore central to understanding the intricacies of the gating mechanism of MS channels. We used a constant-force steered molecular dynamics (SMD) approach to perform unidirectional pulling tests on all the helices of MscL in M. tuberculosis and E. coli homologs. Using this method, we could overcome the issues encountered with the commonly used constant-velocity SMD simulations, such as low mechanical stability of the helix during... 

    Investigation of properties of polyethylene/clay nanocomposites prepared by new in situ ziegler-natta catalyst

    , Article Materials and Design ; Volume 30, Issue 7 , 2009 , Pages 2309-2315 ; 02641275 (ISSN) Nikkhah, S. J ; Ramazani Saadat Abadi, A ; Baniasadi, H ; Tavakolzadeh, F ; Sharif University of Technology
    2009
    Abstract
    This paper is devoted to investigation of morphological and physical-mechanical properties of polyethylene (PE)/clay nanocomposites prepared via in situ polymerization method using bi-supported Ziegler-Natta catalyst. Bentonite type clay and MgCl2 (ethoxide type) were used as the support of TiCl4. Catalyst support and polymerization process have been done in slurry phase using Triisobutylaluminum as the co-catalyst. The microstructure of the nanocomposites was examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM indicated that almost fully exfoliated PE/clay nanocomposites were produced successfully using this method. According to permeability...