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    Ballistic molecular transport through two-dimensional channels

    , Article Nature ; Volume 558 , 20 June , 2018 , Pages 420-423 ; 00280836 (ISSN) Keerthi, A ; Geim, A. K ; Janardanan, A ; Rooney, A. P ; Esfandiar, A ; Hu, S ; Dar, S. A ; Grigorieva, I. V ; Haigh, S. J ; Wang, F. C ; Radha, B ; Sharif University of Technology
    Nature Publishing Group  2018
    Gas permeation through nanoscale pores is ubiquitous in nature and has an important role in many technologies 1,2 . Because the pore size is typically smaller than the mean free path of gas molecules, the flow of the gas molecules is conventionally described by Knudsen theory, which assumes diffuse reflection (random-angle scattering) at confining walls 3-7 . This assumption holds surprisingly well in experiments, with only a few cases of partially specular (mirror-like) reflection known 5,8-11 . Here we report gas transport through ångström-scale channels with atomically flat walls 12,13 and show that surface scattering can be either diffuse or specular, depending on the fine details of the... 

    Improving mixed-matrix membrane performance: Via PMMA grafting from functionalized NH2-UiO-66

    , Article Journal of Materials Chemistry A ; Volume 6, Issue 6 , 2018 , Pages 2775-2791 ; 20507488 (ISSN) Molavi, H ; Shojaei, A ; Mousavi, S. A ; Sharif University of Technology
    Royal Society of Chemistry  2018
    The major obstacles in gas separation by mixed-matrix membranes (MMMs) are poor dispersion and poor affinity between polymers and fillers. The present study demonstrates that these challenges can be overcome appropriately by utilizing a series of synthesized stand-alone MMMs. The matrix used was polymethyl methacrylate (PMMA) and the MMMs were synthesized by in situ polymerization of methyl methacrylate (MMA) in the presence of UiO-66, NH2-UiO-66 and vinyl group attached UiO-66. In situ polymerization of MMA in the presence of vinyl attached UiO-66 resulted in PMMA grafted UiO-66 with a high degree of grafting. Microscopic analysis by field emission scanning electron microscopy (FESEM)... 

    Experimental and numerical investigation on the jet characteristics of spark ignition direct injection gaseous injector

    , Article Applied Energy ; Volume 105 , 2013 , Pages 8-16 ; 03062619 (ISSN) Chitsaz, I ; Saidi, M. H ; Mozafari, A. A ; Hajialimohammadi, A ; Sharif University of Technology
    Natural gas has widely been used as a fuel in conventional Diesel and spark ignition engines. The better understanding of injector parameters on the jet structure is helpful for the combustion optimization. This paper presents an experimental and numerical study on the jet structure of gaseous fuel injector in spark ignition direct injection engine by Schlieren technique and numerical procedure. Helium was injected through a gaseous injector at the different pressure ratios and nozzle diameters to understand the effects of nozzle geometry and pressure ratio for a dedicated correlation of CNG-SIDI injector. It was found that higher pressure ratio and exit nozzle diameter led to more tip... 

    Production of silver nanoparticles by electromagnetic levitation gas condensation

    , Article Chemical Engineering Journal ; Volume 168, Issue 1 , March , 2011 , Pages 441-445 ; 13858947 (ISSN) Malekzadeh, M ; Halali, M ; Sharif University of Technology
    Electromagnetic levitation gas condensation (ELGC) method was used to synthesize silver nanoparticles (NPs). Silver droplets were melted and levitated stably at about 1130°C with appropriate flat coils in a 10mm OD silica tube. High purity argon, nitrogen and helium were employed as carrier gases and cooling media. Morphology and particle size of the products were investigated by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX) and dynamic light scattering (DLS). The DLS, SEM and TEM studies demonstrated narrow size distribution of spherical shape silver NPs with mean particle size of about 60, 50 and 30nm... 

    Studying dynamic pull-in behavior of microbeams by means of the homotopy analysis method

    , Article 2008 ASME International Mechanical Engineering Congress and Exposition, IMECE 2008, Boston, MA, 31 October 2008 through 6 November 2008 ; Volume 13, Issue PART A , 2009 , Pages 129-135 ; 9780791848746 (ISBN) Moghimi Zand, M ; Tajalli, S. A ; Ahmadian, M. T ; Sharif University of Technology
    In this study, the homotopy analysis method (HAM) is used to study dynamic pull-in instability in microbeams considering different sources of nonlinearity. Electrostatic actuation, fringing field effect and midplane stretching causes strong nonlinearity in microbeams. In order to investigate dynamic pull-in behavior, using Galerkin's decomposition method, the nonlinear partial differential equation of motion is reduced to a single nonlinear ordinary differential equation. The obtained equation is solved analytically in time domain using HAM. The problem is studied by two separate manners: direct use of HAM and indirect use of HAM in conjunction with He's Modified Lindstedt- Poincaré Method.... 

    Automated trace determination of earthy-musty odorous compounds in water samples by on-line purge-and-trap-gas chromatography-mass spectrometry

    , Article Journal of Chromatography A ; Volume 1136, Issue 2 , 2006 , Pages 170-175 ; 00219673 (ISSN) Salemi, A ; Lacorte, S ; Bagheri, H ; Barceló, D ; Sharif University of Technology
    An automated technique based on purge-and-trap coupled to gas chromatography with mass spectrometric detection has been developed and optimized for the trace determination of five of the most important water odorants; 2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, 2-methylisoborneol, 2,4,6-trichloroanisole and geosmin. The extraction method was absolutely solvent-free. Analytes were purged from 20 ml of water sample containing sodium chloride at room temperature by a flow of He and trapped on a Tenax sorbent. The desorption step was performed with helium and temperature programming and desorbed analytes were directly transferred to a gas chromatograph coupled to a mass...