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diffusion
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Reaction-diffusion equations with polynomial drifts driven by fractional brownian motions
, Article Stochastic Analysis and Applications ; Volume 28, Issue 6 , Oct , 2010 , Pages 1020-1039 ; 07362994 (ISSN) ; Sharif University of Technology
2010
Abstract
A reaction-diffusion equation on [0, 1]d with the heat conductivity k > 0, a polynomial drift term and an additive noise, fractional in time with H > 1/2, and colored in space, is considered. We have shown the existence, uniqueness and uniform boundedness of solution with respect to k Also we show that if k tends to infinity, then the corresponding solutions of the equation converge to a process satisfying a stochastic ordinary differential equation
Numerical simulation of electro-deposition process influenced by force convection and migration of ions
, Article Journal of Electroanalytical Chemistry ; Volume 782 , 2016 , Pages 117-124 ; 15726657 (ISSN) ; Saidi, M. S ; Sani, M ; Sharif University of Technology
Elsevier B.V
2016
Abstract
Electro-deposition process is one of the main steps in the LIGA procedure to fabricate microstructures. In this paper, one-dimensional modeling of Nickel electro-deposition process is implemented on Rayan and developed for simulation of time-dependence diffusion and migration of charge species with reduction reactions on the cathode surface. This model is proposed by considering governing equations on electro-kinetic phenomena consist of Nernst-Plank equation and Poisson's equation of electric potential. Transport of ions toward the cathode is considered based on the effect of convection, reaction rate, diffusion and migration. The numerical results cover two series of data consisting of...
A study on the effects bonding temperature and holding time on mechanical and metallurgical properties of al–cu dissimilar joining by DFW
, Article Transactions of the Indian Institute of Metals ; Volume 70, Issue 1 , 2017 , Pages 125-131 ; 09722815 (ISSN) ; Paidar, M ; Youzbashi zade, H ; Sharif University of Technology
Springer India
2017
Abstract
The aim of this study was to evaluate the influence of bonding temperature and holding time on the metallurgical and mechanical properties for weld joints of 5 mm aluminum to copper using Sn interlayer. The bonding temperature varied from 500 to 600 °C whilst the holding time varied from 30 to 120 min under 8 MPa uniaxial load in 1 × 10−4 torr vacuum. The microstructure analysis, phase analysis and distribution of elements in the interface were performed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and element map analysis. It was found that diffusion welding parameters had a significant effect on shear strength. The attained data of tensile strength tests showed...
SN transport method for neutronic noise calculation in nuclear reactor systems: comparative study between transport theory and diffusion theory
, Article Annals of Nuclear Energy ; Volume 114 , 2018 , Pages 236-244 ; 03064549 (ISSN) ; Vosoughi, N ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
In this paper, the neutron noise based on transport theory and diffusion noise theory using Green's function technique is calculated. As the neutron noise is used for core diagnostic, surveillance and monitoring, calculation of neutron noise precisely can play an important role in monitoring and safety. We compare the accuracy of Green's function based on transport and diffusion theory in order to survey the differences between these theories. In this study some deviation between results obtained two theories are observed, and the impact of dimensions, cross sections and frequency on the results investigated. © 2017
Role of base-metal composition in isothermal solidification during diffusion brazing of nickel-based superalloys
, Article Science and Technology of Welding and Joining ; Volume 23, Issue 1 , 2018 , Pages 13-18 ; 13621718 (ISSN) ; Ekrami, A ; Kokabi, A. H ; Sharif University of Technology
Taylor and Francis Ltd
2018
Abstract
The key feature of diffusion brazing, also referred to as transient liquid phase bonding, is isothermal solidification which precludes the formation of intermetallic in the joint centreline. Analysing the available data published in the literature showed that the composition of the nickel-based superalloys plays a strong role in determining the required time for obtaining intermetallic-free joint during diffusion brazing. This effect is not predictable by the standard conventional models. It is proposed that increasing the boride-forming elements in the base superalloy which promotes in situ boride precipitation at the diffusion-affected zone can accelerate the diffusion flux of the boron...
Drift-diffusion explains response variability and capacity for tracking objects
, Article Scientific Reports ; Volume 9, Issue 1 , 2019 ; 20452322 (ISSN) ; Azarnoush, H ; Towhidkhah, F ; Gohari, A ; Ghazizadeh, A ; Sharif University of Technology
Nature Publishing Group
2019
Abstract
Being able to track objects that surround us is key for planning actions in dynamic environments. However, rigorous cognitive models for tracking of one or more objects are currently lacking. In this study, we asked human subjects to judge the time to contact (TTC) a finish line for one or two objects that became invisible shortly after moving. We showed that the pattern of subject responses had an error variance best explained by an inverse Gaussian distribution and consistent with the output of a biased drift-diffusion model. Furthermore, we demonstrated that the pattern of errors made when tracking two objects showed a level of dependence that was consistent with subjects using a single...
How chassis structure and substrate crystalline direction affect the mobility of thermally driven p-carborane-wheeled nanocars
, Article Journal of Physical Chemistry C ; Volume 123, Issue 8 , 2019 , Pages 4805-4824 ; 19327447 (ISSN) ; Nejat Pishkenari, H ; Meghdari, A ; Sharif University of Technology
American Chemical Society
2019
Abstract
In recent years, various nanocars have been synthesized in order to provide controlled mechanical function, transport other nanoparticles, or enable bottom-up assembly capability. There have even been racing competitions among well-known nanocars in which the wheels play an influential role. In this paper, the motion of thermally driven nanocars equipped with p-carborane wheels on Au(111) and Au(001) substrates is investigated. For the sake of comparison, classical all-atom molecular dynamics (MD) and rigid-body MD (RBMD) have been used to study the motion threshold as well as to analyze the effect of temperature, substrate crystalline direction, and chassis shape on the diffusive motion of...
How chassis structure and substrate crystalline direction affect the mobility of thermally driven p-carborane-wheeled nanocars
, Article Journal of Physical Chemistry C ; 2019 ; 19327447 (ISSN) ; Pishkenari, H. N ; Meghdari, A ; Sharif University of Technology
American Chemical Society
2019
Abstract
In recent years, various nanocars have been synthesized in order to provide controlled mechanical function, transport other nanoparticles, or enable bottom-up assembly capability. There have even been racing competitions among well-known nanocars in which the wheels play an influential role. In this paper, the motion of thermally driven nanocars equipped with p-carborane wheels on Au(111) and Au(001) substrates is investigated. For the sake of comparison, classical all-Atom molecular dynamics (MD) and rigid-body MD (RBMD) have been used to study the motion threshold as well as to analyze the effect of temperature, substrate crystalline direction, and chassis shape on the diffusive motion of...
Microstructural investigation of the coatings prepared by simultaneous aluminizing and siliconizing process on γ-TiAl
, Article Journal of Mining and Metallurgy, Section B: Metallurgy ; Volume 55, Issue 2 , 2019 , Pages 217-225 ; 14505339 (ISSN) ; Azadeh, M ; Sharif University of Technology
Technical Faculty in Bor
2019
Abstract
In this research, formation of aluminide/silicide diffusion coatings on γ -TiAl[Ti-48Al-2Nb-2Cr (at.%)] alloy using gasphase diffusion pack cementation process has been investigated. The application of powder mixtures with various chemical compositions in the pack cementation process performed at 1000°C for 6 hours in order to achieve simultaneous diffusion of Al and Si, showed that the composition of the powder mixture could have a significant effect on the structure and thickness of the aluminide/silicide coatings. The identification and analysis of aluminide/silicide microstructures formed as a result of simultaneous diffusion of Al and Si, which was comprehensively and qualitatively done...
Three-dimensional spread analysis of a Dengue disease model with numerical season control
, Article International Journal of Biomathematics ; Volume 14, Issue 8 , 2021 ; 17935245 (ISSN) ; Hesaaraki, M ; Sharif University of Technology
World Scientific
2021
Abstract
Dengue is among the most important infectious diseases in the world. The main contribution of our paper is to present a mixed system of partial and ordinary differential equations. This combined model is a generalization of the two presented mathematical models (A. L. de Araujo, J. L. Boldrini and B. M. Calsavara, An analysis of a mathematical model describing the geographic spread of dengue disease, J. Math. Anal. Appl. 444 (2016) 298-325) and (L. Cai, X. Li, N. Tuncer, M. Martcheva and A. A. Lashari, Optimal control of a malaria model with asymptomatic class and superinfection, Math. Biosci. 288 (2017) 94-108), describing the geographic spread of dengue disease. Our model has the ability...
Numerical optimization of three-cavity magneto mercury reciprocating (MMR) micropump
, Article Engineering Applications of Computational Fluid Mechanics ; Volume 15, Issue 1 , 2021 , Pages 1954-1966 ; 19942060 (ISSN) ; Mofakham, A. A ; Shafii, M. B ; Sharif University of Technology
Taylor and Francis Ltd
2021
Abstract
The operation of the three-cavity magneto mercury reciprocating (MMR) micropump, whose prototype were presented in an earlier companion paper, was numerically explored. In the three-cavity MMR micropump, three mercury slugs are moved by a periodic Lorentz force with a phase difference in three separate cavities. A consecutive motion of the slugs in their cavities transfer air from the inlet to the outlet. Two-dimensional OpenFOAM simulations were carried out to explore the influence of electric current excitation phase difference and back-pressure. The numerical simulations predicted the MMR micropump (with no valve) with a phase difference of (Formula presented.) and (Formula presented.)...
A model reduction based approach for extracting the diffusion and generation terms of pn junction leakage current
, Article Semiconductor Science and Technology ; Volume 18, Issue 4 , 2003 , Pages 234-240 ; 02681242 (ISSN) ; Fathololoumi, S ; Rashidian, B ; Sharif University of Technology
2003
Abstract
Using a model reduction method, a formula for the ideality factor of a pn junction as a function of the diffusion and generation terms of its reverse current is derived. Using this formula a method for separate computation of these two currents for a pn junction is presented. The validity of the method is investigated using computer simulations for an assumed diode with known ideality factor and total leakage current. Experimental results for two commercially available diodes validate the proposed technique
Deactivation behavior of the catalyst in solid acid catalyzed alkylation: Effect of pore mouth plugging
, Article Chemical Engineering Science ; Volume 57, Issue 17 , 2002 , Pages 3611-3620 ; 00092509 (ISSN) ; Kazemeini, M ; Khorasheh, F ; Badakhshan, A ; Sharif University of Technology
2002
Abstract
The deactivation of solid acid catalysts in liquid-phase alkylation of isobutane with butenes was investigated. The role of pore mouth plugging, in particular, was studied and it was found that it had a significant effect on the deactivation behavior. Simple explicit correlations were developed for catalyst lifetime in a CSTR, both in terms of time-on-stream and butene turnover per catalyst weight. The correlations were tested using available experimental data from the literature and a reasonable agreement was observed. It was shown that for a zeolitic catalyst the butene turnover per catalyst weight was proportional to the square root of catalyst loading, while it was inversely proportional...
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) ; 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 ; 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...
The characteristics of serrated flow in superalloy IN738LC
, Article Materials Science and Engineering A ; Volume 486, Issue 1-2 , 2008 , Pages 376-380 ; 09215093 (ISSN) ; Asgari, S ; Sharif University of Technology
2008
Abstract
Serrated flow was investigated in superalloy IN738LC, a nickel-base γ′ age-hardened alloy. In this material serrated flow appeared between 350 and 450 °C and strain rate of (8.77 × 10-5 to 8.77 × 10-3) s-1. Activation energy for this process was calculated to be 0.69-0.86 eV which is in good agreement with the values reported for similar alloys. Results show that the diffusion rate of substitutional solute atoms at this temperature range is too low to cause this effect. This suggests that the interaction of solute atoms and moving dislocation is responsible for the observed serrated flow in this alloy. © 2007 Elsevier B.V. All rights reserved
The effect of Si addition and Ta diffusion barrier on growth and thermal stability of NiSi nanolayer
, Article Microelectronic Engineering ; Volume 85, Issue 3 , 2008 , Pages 548-552 ; 01679317 (ISSN) ; Akhavan, O ; Moshfegh, A. Z ; Sharif University of Technology
2008
Abstract
Formation and thermal stability of nanothickness NiSi layer in Ni(Pt 4 at.%)/Si(1 0 0) and Ni0.6Si0.4(Pt 4 at.%)/Si(1 0 0) structures have been investigated using magnetron co-sputtering deposition method. Moreover, to study the effect of Si substrate in formation of NiSi and its thermal stability, we have used Ta diffusion barrier between the Ni0.6Si0.4 layer and the Si substrate. Post annealing treatment of the samples was performed in an N2 environment in a temperature range from 200 to 900 °C for 2 min. The samples were analyzed by four point probe sheet resistance (Rs) measurement, X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. It was found that the annealing...
Inverse design of supersonic diffuser with flexible walls using a Genetic Algorithm
, Article Journal of Fluids and Structures ; Volume 22, Issue 4 , 2006 , Pages 529-540 ; 08899746 (ISSN) ; Ziaei-Rad, M ; Sharif University of Technology
2006
Abstract
An efficient algorithm for the design optimization of the compressible fluid flow problem through a flexible structure is presented. The methodology has three essential parts: first the behavior of compressible flow in a supersonic diffuser was studied numerically in quasi-one-dimensional form using a flux splitting method. Second, a fully coupled sequential iterative procedure was used to solve the steady state aeroelastic problem of a flexible wall diffuser. Finally, a robust Genetic Algorithm was implemented and used to calculate the optimum shape of the flexible wall diffuser for a prescribed pressure distribution. © 2006 Elsevier Ltd. All rights reserved
Effect of Zr addition on the aging behavior of A319 aluminum cast alloy
, Article Scripta Materialia ; Volume 52, Issue 4 , 2005 , Pages 253-257 ; 13596462 (ISSN) ; Mahmudi, R ; Khomamizadeh, F ; Sharif University of Technology
2005
Abstract
The structure, age hardening response, precipitate type and hardness of A319 cast aluminum alloy without and with zirconium addition were investigated. The as-solutionized and artificially-aged hardness values were higher for the Zr-containing alloy. This is believed to be a consequence of the precipitation of Al3Zr particles produced during sufficiently long solutionizing treatments. © 2004 Acta Materialia Inc. Published by 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) ; 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...