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    A calculation of diffusion parameters for Cu/Ta and Ta/Si interfaces in Cu/Ta/Si(1 1 1) structure

    , Article Materials Science in Semiconductor Processing ; Volume 6, Issue 4 , 2003 , Pages 165-170 ; 13698001 (ISSN) Moshfegh, A. Z ; Akhavan, O ; Sharif University of Technology
    2003
    Abstract
    In this investigation, we have studied the elemental diffusion coefficients of the Cu/Ta and Ta/Si interfaces in the Cu/Ta/Si(1 1 1) structure. The diffusion parameters for Cu diffusion into the Ta barrier layer, Ta diffusion into the Si substrate and diffusion of Si atoms into the Ta layer have been calculated using conversion of RBS data to concentration-depth profile curves and the solution of Fick's equation based on a constant diffusing amount boundary conditions. Furthermore, by calculating grain boundary diffusion coefficients, we have estimated grain boundary slabs of the Ta layer at different temperatures. It was shown that, the width of grain boundary slabs in the Ta layer at 700°C... 

    Modification of square root formula for approximate estimation of diffusion coefficient of particulate adsorbents

    , Article ICCCE 2010 - 2010 International Conference on Chemistry and Chemical Engineering, Proceedings, 1 August 2010 through 3 August 2010, Kyoto ; 2010 , Pages 110-113 ; 9781424477647 (ISBN) Outokesh, M ; Grayeli, F ; Tayyebi, A ; Khanchi, A ; Sharif University of Technology
    2010
    Abstract
    The well known square root formula for the kinetics of adsorption by spherical particle U(t)=6/r0(Dt/π)1/2 is only valid in the early stage of adsorption (U(t) ≤ 0.3), where U(t) shows fractional attainment to the equilibrium. Present study shows that with a little manipulation of this formula, its application range can be extended to U (t) ≤ 0.95. The suggested formula U(t)=6/r0(Dt/π)1/2 -3Dt/r0 2 in addition of simplicity, has higher accuracy than both square root and Vermeulen's formulas  

    The determination of effective diffusivity coefficients in a solvent gas heavy oil system for methane

    , Article Petroleum Science and Technology ; Volume 30, Issue 24 , 2012 , Pages 2582-2593 ; 10916466 (ISSN) Zamanian, E ; Dadvar, M ; Kharrat, R ; Ghazanfari, M. H ; Sharif University of Technology
    2012
    Abstract
    In this investigation, an accurate high pressure and temperature diffusion setup was applied to measure the diffusion coefficients of methane in Iranian heavy oils in presence and absence of porous media by using the pressure-decay method. The solvent diffusivity in heavy oil was determined by both graphical and numerical methods. In addition, the effects of the porous medium and the temperature on the molecular diffusion coefficient of the solvent gas in the liquid phase were discussed and finally, using experimental data, a functionality dependence of molecular diffusivity on temperature and porous medium characteristics was proposed  

    Investigation of a new mean temperature-dependent potential energy function for methane and its use for the prediction of transport properties

    , Article Molecular Physics ; Volume 105, Issue 10 , 2007 , Pages 1453-1463 ; 00268976 (ISSN) Nahaly, M ; Parsafar, G. A ; Goharshadi, E. K ; Sharif University of Technology
    2007
    Abstract
    In this work an improved mean potential energy function for the interaction of an isolated pair of methane is obtained, from which the non-equilibrium properties of methane at zero pressure limit are calculated, accurately. The potential energy function of 21 different fixed orientations of (CH4)2 dimer has been obtained via the coupled cluster method. In order to obtain a mean potential energy function, the Boltzmann-average of the obtained potentials of the selected fixed orientations has been used. Unlike the full potential energy surface with the angle-dependent, the parameters of the mean potential are found to be temperature-dependent. The mean potential energy function is fitted well... 

    Kinetic parameters estimation of MgO-C refractory by shrinking core model

    , Article Journal of Materials Science and Technology ; Volume 22, Issue 6 , 2006 , Pages 826-832 ; 10050302 (ISSN) Hashemi, B ; Nemati, Z. A ; Sadrnezhaad, S. K ; Moghimi, Z. A ; Sharif University of Technology
    2006
    Abstract
    Kinetics of oxidation of MgO-C refractories was investigated by shrinking core modeling of the gas-solid reactions taking place during heating the porous materials to the high temperatures. Samples containing 4.5-17 wt pct graphite were isothermally oxidized at 1000-1350°C. Weight loss data was compared with predictions of the model. A mixed 2-stage mechanism comprised of pore diffusion plus boundary layer gas transfer was shown to generally control the oxidation rate. Pore diffusion was however more effective, especially at graphite contents lower than 10 wt pct under forced convection blowing of the air. Model calculations showed that effective gas diffusion coefficients were in the range... 

    A macroscopic traffic flow model that includes driver sensitivity to the number of free spaces ahead

    , Article Transportmetrica B ; 2017 , Pages 1-17 ; 21680566 (ISSN) Pour, I. M ; Nassiri, H ; Sharif University of Technology
    Abstract
    This paper addresses the first-order extension of the Lighthill–Whitham– Richards (LWR) macroscopic traffic flow model. Although previous studies have focused on the fluid aspect of traffic flow, none have addressed the sensitivity of drivers to the number of free spaces within a certain distance ahead of the subject driver. To incorporate driver behavior, we used the number of free spaces ahead of subject drivers and their sensitivity to the number of free spaces within a certain distance ahead. The resulting model is a convection-diffusion model. By computing Einstein's diffusion equation and comparing it with the diffusion coefficient in the extended model, a theoretical relation for the... 

    A macroscopic traffic flow model that includes driver sensitivity to the number of free spaces ahead

    , Article Transportmetrica B ; Volume 8, Issue 1 , 2020 , Pages 290-306 Pour, I. M ; Nassiri, H ; Sharif University of Technology
    Taylor and Francis Ltd  2020
    Abstract
    This paper addresses the first-order extension of the Lighthill–Whitham– Richards (LWR) macroscopic traffic flow model. Although previous studies have focused on the fluid aspect of traffic flow, none have addressed the sensitivity of drivers to the number of free spaces within a certain distance ahead of the subject driver. To incorporate driver behavior, we used the number of free spaces ahead of subject drivers and their sensitivity to the number of free spaces within a certain distance ahead. The resulting model is a convection-diffusion model. By computing Einstein's diffusion equation and comparing it with the diffusion coefficient in the extended model, a theoretical relation for the... 

    A Langevin equation for the rates of currency exchange based on the Markov analysis

    , Article Physica A: Statistical Mechanics and its Applications ; Volume 385, Issue 2 , 2007 , Pages 601-608 ; 03784371 (ISSN) Farahpour, F ; Eskandari, Z ; Bahraminasab, A ; Jafari, G. R ; Ghasemi, F ; Sahimi, M ; Reza Rahimi Tabar, M ; Sharif University of Technology
    2007
    Abstract
    We propose a method for analyzing the data for the rates of exchange of various currencies versus the U.S. dollar. The method analyzes the return time series of the data as a Markov process, and develops an effective equation which reconstructs it. We find that the Markov time scale, i.e., the time scale over which the data are Markov-correlated, is one day for the majority of the daily exchange rates that we analyze. We derive an effective Langevin equation to describe the fluctuations in the rates. The equation contains two quantities, D(1) and D(2), representing the drift and diffusion coefficients, respectively. We demonstrate how the two coefficients are estimated directly from the... 

    Accurate analytical model for determination of effective diffusion coefficient of polymer electrolyte fuel cells by designing compact Loschmidt cells

    , Article Fuel ; Volume 199 , 2017 , Pages 551-561 ; 00162361 (ISSN) Izadmehr, M ; Abbasi, M ; Mansouri, M ; Kazemi, A ; Nakhaee, A ; Daryasafar, A ; Sharif University of Technology
    Elsevier Ltd  2017
    Abstract
    Effective diffusion coefficient is an important parameter which needs to be determined in different fields of study, such as cathode catalyst layers of PEM fuel. For this purpose, a Loschmidt diffusion cell can be used. When a porous medium is placed in Loschmidt apparatus, the effective gas diffusion coefficient (EGDC) of this section must be correlated by diffusion coefficient in absence of a porous medium. In the previous researches studying the Loschmidt diffusion cell, a simplifying infinite-length assumption was used in the analytical solution. Therefore, the solution is only applicable for a short time range, and this can result in high error. In order to overcome this challenge, the... 

    Finding Influential Nodes in Complex Networks

    , M.Sc. Thesis Sharif University of Technology Barazandeh Shirvan, Amin (Author) ; Jalili, Mahdi (Supervisor)
    Abstract
    The modern science of networks helps us to have a better understanding of complex systems. Networked systems can be found everywhere and many systems can be represented by a complex network. A networked structure consists of a number of nodes and links connecting to them. Networks’ ability in information propagation is one of their amazing features that have attracted lots of scholars to work on. It has potential applications in many fields ranging from marketing to biology, epidemiology and sociology. Information propagation studies how information such as computer viruses, contagion, rumor, or new product’s interest propagates over a network. Percolation theory and various epidemic models... 

    Experimental Analysis of Water Seepage in RCC Dams and Determination of Its Repair and Improvement Methods

    , M.Sc. Thesis Sharif University of Technology Heydarnezhad, Fatemeh (Author) ; Ghaemian, Mohsen (Supervisor) ; Toufigh, Vahab (Supervisor)
    Abstract
    In this study, the effect of mix design parameters and the mechanical properties of roller-compacted concrete (RCC) were considered to evaluate its water permeability coefficient. For this purpose, over 400 laboratory specimens were prepared and tested. A formula was proposed to predict the permeability coefficient of RCC by considering the main parameters. Moreover, artificial neural network (ANN) was constructed to model the permeability coefficient of RCC based on its mix design constituents and the test results. The algorithm obtained from tests results were verified independently using extra specimens. Furthermore, Taguchi method and analysis of variance (ANOVA) were used to determine... 

    Separation of CO2 Using Mixed Matrix Rubbery Membrane

    , M.Sc. Thesis Sharif University of Technology Arbabpour Jannatabadi, Atiyeh (Author) ; Bastani, Dariush (Supervisor) ; Ghadimi, Ali (Supervisor)
    Abstract
    In this study, ZIF-8 was synthesized at room temperature and Then ZIF-8/PEGDA mixed matrix membranes with 5 and 10% of ZIF-8 were prepared by UV photopolymerization to analyze the separation CO2 from natural gas for the first time. The permeation results of gases in mixed matrix membranes in the temperature range of 35-75 degrees centigrade and in pressure ranging from 4-15 bar show the permeability of gases in mixed matrix membranes with 5 and 10% increase more than a pure polymer nearly 14.3 and 31%, respectively, But, CO2=CH4 selectivity decreases. The gas sorption in ZIF-8 was measured in the temperature range up to 75 ◦C and pressure ranging from 2-5 bar. The adsorption isotherm follows... 

    Using Supported Ionic Liquid Membranes (SILMs) for Selective Separation of CO2/CH4

    , M.Sc. Thesis Sharif University of Technology M.Barghi, Hamed (Author) ; Rashtchian ,Davood (Supervisor) ; Adibi, Mina (Supervisor)
    Abstract
    Supported Ionic Liquid Membranes (SILMs) are fabricated by saturating the pores of a porous support with ionic liquids. To assess the performance of SILMS, it is necessary to obtain data about the properties of ionic liquids such as diffusivity, solubility, and etc. To accomplish this task, in this project the permeability and diffusivity of CO2 and CH4 through three immidazolium-based ionic liquids: [bmim][PF6], [hmim][Tf2N], and "1-methyl-3-(3- tri methoxi silil propyl) imidazolium bis (tri fluoro methyl solphonyl)" , in the temperature range between 27-45 ℃ and pressures within 10-50 kPa, are measured. It is shown in data validation section that the results of this study are in good... 

    Measurement of Gas Permeation Though Carbonized Membranes and Determination of Mass Transfer Mechanisms

    , M.Sc. Thesis Sharif University of Technology Pakdaman, Ehsan (Author) ; Ghotbi, Cyrus (Supervisor) ; Taghikhani, Vahid (Supervisor) ; Mahdyarfar, Mohammad (Supervisor)
    Abstract
    In this project, using experimental results for permeation of gases H2, He, N2, and CO on a microporous membrane (the applied sample was a ceramic membrane) and modified equations, pore diameter, tortuosity, and porosity were determined for this type of membrane. Furthermore, pore diameter, critical volume, and characteristic energy of a carbon molecular sieve membrane were calculated using experimental data for CO2 adsorption on this type of membrane. Diffusivities of CO2, N2, and Ar were also calculated by means of the uptake, time lag/adsorption, and permeability/adsorption tests on carbon molecular sieve membranes utilizing experimental data obtained for this type of membranes and the... 

    The Synthesis and Characterization of Nano Zeolitic Molecular Sieve for Separation of 133Xe from 85Kr

    , Ph.D. Dissertation Sharif University of Technology Charkhi, Amir (Author) ; Kazemeini, Mohammad (Supervisor) ; Ahmadi, Javad (Supervisor)
    Abstract
    In this study the feasibility of xenon separation from xenon-krypton mixture was investigated by utilizing of the chromatographic column filled with nano and micron sized NaY zeolite. For this purpose the nano NaY with the yield of 100% related to Al2O3 and the average size of 98.6 nm was synthesized through the clear solution method with the mid-adding of NaOH. Furthermore, a novel method for granulation of nano zeolite was developed by utilizing sodium alginate as an external template. In this method the production of uniform spherical granules with the different sizes in the range of several milimiteres to 100 µm was easily performed. Moreover, the results showed that the adding of... 

    Molecular Dynamics Simulation of Nanocar Motion on Carbon Structures

    , Ph.D. Dissertation Sharif University of Technology Mofidi, Mahsa (Author) ; Nejat Pishkenari, Hossein (Supervisor) ; Ejtehadi, Mohammad Reza (Supervisor)
    Abstract
    Nanomachines are molecules inspired by natural molecular machines and are able to move and transport at the nanoscale. Due to the advancement of nanotechnology, the need to move materials and energy on a small scale is necessary more than ever. Nanocars are artificial molecular machines with chassis, axles, and wheels designed for nanoscale transport at materials’ surfaces. Understanding the dependence of surface dynamics of nanocars on the substrate’s physico-chemical properties is critical to the design of the transport properties of such man-made nanoscale devices. Among the multitude of potential substrates for the nanotransporters, graphene exhibits intrinsic ripples on its surface,... 

    Banks Money Creation and the Transmission Mechanism of Shocks

    , M.Sc. Thesis Sharif University of Technology Esfahani, Mohammad Reshad (Author) ; Madanizadeh, Ali (Supervisor) ; Mahmoodzadeh, Amineh (Supervisor)
    Abstract
    Banks are not only money brokers but also money creators. The ability of a bank to create money is due to its unique feature in issuing debts (deposits) that are accepted as a medium of exchange by economic agents. Although this bank function has been discussed under the "liquidity transformation" heading under the micro-banking literature, it has been less discussed in macro literature. In this study, we want to examine the consequences of the bank's liquidity transformation function by developing a New-Keynesian model in which banks can finance the economy by voluntarily expanding their balance sheet. To identify the mechanisms that the money creator bank creates in the model, we have... 

    Computation of some thermodynamic properties of nitrogen using a new intermolecular potential from molecular dynamics simulation

    , Article Chemical Physics ; Volume 358, Issue 3 , 2009 , Pages 185-195 ; 03010104 (ISSN) Kafshdar Goharshadi, E ; Abbaspour, M ; Namayandeh Jorabchi, M ; Nahali, M ; Sharif University of Technology
    2009
    Abstract
    A new pair-potential energy function of nitrogen has been determined via the inversion of reduced viscosity collision integrals and fitted to obtain an analytical potential form. The pair-potential reproduces the second virial coefficient, viscosity, thermal conductivity, self-diffusion coefficient, and thermal diffusion factor of nitrogen in a good accordance with experimental data over wide ranges of temperatures and densities. We have also performed the molecular dynamics simulation to obtain pressure, internal energy, heat capacity at constant volume, and self-diffusion coefficient of nitrogen at different temperatures and densities using our calculated pair-potential and some other... 

    Monte Carlo simulation and benchmarking of pulsed neutron experiments in variable buckling Beo systems

    , Article Annals of Nuclear Energy ; Volume 36, Issue 5 , 2009 , Pages 547-549 ; 03064549 (ISSN) Sohrabpour, M ; Ezzati, A. O ; Sharif University of Technology
    2009
    Abstract
    Pulsed neutron decay simulation of BeO moderator as a result of injecting 14 MeV neutron pulses into finite size systems are carried out with the MCNP Monte Carlo code. The simulated decay constants as compared against a previous experimental work showed variations of about 2%. The resulting decay constants and the fitted diffusion coefficients based on the simulation results are found to agree with the experimental results within a margin of about 4%. © 2009 Elsevier Ltd. All rights reserved  

    A new empirical correlation for predicting effective molecular diffusivity of gas-heavy oil-porous media systems

    , Article Special Topics and Reviews in Porous Media ; Volume 3, Issue 1 , 2012 , Pages 23-33 ; 21514798 (ISSN) Zamanian, E ; Mirjordavi, N ; Kazemeini, M ; Ghazanfari, M. H ; Sharif University of Technology
    2012
    Abstract
    Molecular diffusivity is an essential parameter for modeling of mass transfer in enhanced oil recovery processes. However, experimentally determined diffusivities for light gas-heavy oil systems in the presence of porous media are relatively rare. A few correlations are available in the literature that predict diffusivity of gases into heavy oil in presence of porous media. In this work the pressure-decay method was applied to obtain effective molecular diffusion of CO 2, CH 4 and N 2-heavy oil systems in both bulk and porous media systems at different temperatures. The diffusivity of gases in heavy oil was determined by matching the numerically calculated pressures to the measured data. A...