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    Enhancement of surface adsorption-desorption rates in microarrays invoking surface charge heterogeneity

    , Article Sensors and Actuators, B: Chemical ; 2016 ; 09254005 (ISSN) Abdollahzadeh, M ; Saidi, M. S ; Sadeghi, A ; Sharif University of Technology
    Elsevier B.V  2016
    Abstract
    This investigation is devoted to the influences of non-uniform wall characteristics on the surface adsorption-desorption rates in an electrokinetic microarray. Utilizing already explored electroosmotic and electrophoretic velocities, the species transport equations are solved by a finite-volume-based numerical approach. Uniform, sinusoidal, and pulse-like distributions of the zeta potential are considered in the analysis. The developed model is validated by comparing the results with those of two analytical solutions that are derived for limiting conditions. The results reveal that, in some cases, the surface charge heterogeneity can reduce the saturation time by more than 60%. The efficacy... 

    Stable transports between stationary random measures

    , Article Electronic Journal of Probability ; Volume 21 , 2016 ; 10836489 (ISSN) Haji-Mirsadegh, M. O ; Khezeli, A ; Sharif University of Technology
    University of Washington 
    Abstract
    We give an algorithm to construct a translation-invariant transport kernel between two arbitrary ergodic stationary random measures on Rd, given that they have equal intensities.As a result, this yields a construction of a shift-coupling of an arbitrary ergodic stationary random measure and its Palm version.This algorithm constructs the transport kernel in a deterministic manner given a pair of realizations of the two measures.The (non-constructive) existence of such a transport kernel was proved in [9].Our algorithm is a generalization of the work of [3], in which a construction is provided for the Lebesgue measure and an ergodic simple point process.In the general case, we limit ourselves... 

    Point-map-probabilities of a point process and Mecke's invariant measure equation

    , Article Annals of Probability ; Volume 45, Issue 3 , 2017 , Pages 1723-1751 ; 00911798 (ISSN) Baccelli, F ; Haji Mirsadeghi, M. O ; Sharif University of Technology
    Institute of Mathematical Statistics  2017
    Abstract
    A compatible point-shift F maps, in a translation invariant way, each point of a stationary point process Φ to some point of Φ. It is fully determined by its associated point-map, f, which gives the image of the origin by F. It was proved by J. Mecke that if F is bijective, then the Palm probability of Φ is left invariant by the translation of -f . The initial question motivating this paper is the following generalization of this invariance result: in the nonbijective case, what probability measures on the set of counting measures are left invariant by the translation of -f ? The point-map-probabilities of Φ are defined from the action of the semigroup of point-map translations on the space... 

    Point-shift foliation of a point process

    , Article Electronic Journal of Probability ; Volume 23 , 2018 ; 10836489 (ISSN) Baccelli, F ; Haji Mirsadeghi, M. O ; Sharif University of Technology
    University of Washington  2018
    Abstract
    A point-shift F maps each point of a point process Φ to some point of Φ. For all translation invariant point-shifts F, the F-foliation of Φ is a partition of the support of Φ which is the discrete analogue of the stable manifold of F on Φ. It is first shown that foliations lead to a classification of the behavior of point-shifts on point processes. Both qualitative and quantitative properties of foliations are then established. It is shown that for all point-shifts F, there exists a point-shift F⊥, the orbits of which are the F-foils of Φ, and which is measure-preserving. The foils are not always stationary point processes. Nevertheless, they admit relative intensities with respect to one... 

    Numerical study on water distribution in different layers of direct methanol fuel cells

    , Article Journal of the Electrochemical Society ; Vol. 161, issue. 8 , 2014 , pp. E3110-E3124 ; ISSN: 00134651 Kalantari, H ; Baghalha, M ; Sharif University of Technology
    Abstract
    In this paper, a two-dimensional, two-phase, isothermal model is presented to investigate the water transport characteristic and water distribution in a direct methanol fuel cell (DMFC) with emphasis on exploring the water distribution in different layers of DMFC. The liquid-gas two-phase mass transport in the porous anode and cathode is formulated based on multi-fluid model in porous media and water and methanol crossover through the membrane are considered with the effect of diffusion, electro-osmotic drag, and convection. The modeling results agree well with the three different experimental data in an extensive range of operation conditions. A parametric study is also performed to examine... 

    A swarm based method for solving transit network design problem

    , Article Australasian Transport Research Forum, ATRF 2013 - Proceedings ; 2013 Bagherian, M ; Massah, S ; Kermanshahi, S ; Sharif University of Technology
    Australasian Transport Research Forum  2013
    Abstract
    In this study, a Discrete Particle Swarm Optimization (DPSO) algorithm is assimilated to solve the Transit Network Design Problem (TNDP). First, A Mixed Integer Model is developed for the TNDP. The solution methodology utilized here is made of two major elements. A route generation module is firstly developed to generate all the feasible transit lines. Through the second part, a DPSO algorithm is utilized to select the optimal set of lines from the constructed ones. The objective function is to maximize coverage index while satisfying the operator cost upper level constraints. The efficacy and accuracy of the implemented algorithms is compared with ones obtained by an enumeration process as... 

    Bus network design using genetic algorithm

    , Article 53rd Annual Transportation Research Forum, TRF 2012, 15 March 2012 through 17 March 2012, Tampa, FL ; Volume 1 , 2012 , Pages 210-225 ; 9781622764037 (ISBN) Sadrsadat, H ; Poorzahedi, H ; Haghani, A ; Sharifi, E ; Sharif University of Technology
    2012
    Abstract
    The bus network design problem is an important problem in transportation planning. It is the problem of determining a network of bus lines which best achieves a predetermined objective. This may be done with or without the presence of rapid transit lines. This study is devoted to solving this problem using genetic algorithm. The fitness function is defined as the benefit to the users of the bus network less the cost of the operator of the network, which is to be maximized subject to constraints that properly distribute bus routes over the study area. Objective function calculation depends on the basic data of the city and its bus lines and does not need traffic assignment results. So, it is... 

    A simple model of intimal thickening-effects of hypertension

    , Article 2012 19th Iranian Conference of Biomedical Engineering, ICBME 2012 ; 2012 , Pages 276-281 ; 9781467331302 (ISBN) Mirbagheri, S. A ; Saidi, M. S ; Firoozabadi, D ; Sharif University of Technology
    2012
    Abstract
    A vast amount of death in the world has been attributed to atherosclerosis. This disease causes plaque formation and finally lack of blood supply to an organ. The prominent aim of this study is proposing an accurate and simple model to investigate the process of arterial wall thickening. In order to investigate LDL (low density lipoprotein) accumulation in arterial wall which is considered the first stage of atherosclerosis, a four layer model for arterial wall consisting of endothelium, intima, IEL and media is presented. All layers are treated as homogenous porous media. The four-layer arterial wall model is the most powerful and reliable tool for modeling LDL transport within arterial... 

    Effects of hypertension on Intima-Media Thickness (IMT); application to a human carotid artery

    , Article Scientia Iranica ; Volume 23, Issue 4 , 2016 , Pages 1731-1740 ; 10263098 (ISSN) Mirbagheri, S. A ; Saidi, M. S ; Sohrabi, S ; Firoozabadi, B ; Banazadeh, M. H ; Sharif University of Technology
    Sharif University of Technology 
    Abstract
    A vast number of deaths in the world have been attributed to atherosclerosis. The prominent aim of this study is proposing an accurate and simple model to investigate the process of arterial wall thickening. In order to investigate LDL (Low Density Lipoprotein) accumulation in arterial wall, a four layer model for arterial wall consisting of endothelium, intima, IEL, and media is presented. All layers are treated as homogenous porous media. This model has been solved both numerically and analytically. Obtained accumulated LDL in the intima is used to calculate oxidized LDL flux. Also, the presented model and clinical data are used to prepare the growth model for arterial wall. Furthermore,... 

    Dual improvement of DNA-directed antibody immobilization utilizing magnetic fishing and a polyamine coated surface

    , Article RSC Advances ; Volume 6, Issue 112 , 2016 , Pages 111210-111216 ; 20462069 (ISSN) Esmaeili, E ; Soleimani, M ; Shamloo, A ; Mahmoudifard, M ; Vossoughi, M ; Sharif University of Technology
    Royal Society of Chemistry  2016
    Abstract
    The present study is aimed at the development of a novel approach based on the magnetic improvement of DNA-directed antibody immobilization to prepare a highly efficient sensing platform. Magnetic nanoparticle substrates with high surface area capture the dual DNA-conjugated antibodies in a solution. This allows overcoming the typical mass transport limitation of the surface-based antibody immobilization. Antibody-magnetic nanoparticle conjugation is based on a robust hybridization between a DNA tether (attached to the antibody) and its complementary sequence (immobilized on the nanoparticle). Conventional antibody immobilization for the detection of proteins is often insignificant for the... 

    Rarefaction effects on gas mixing in micro- and nanoscales

    , Article ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer, MNHMT 2016, 4 January 2016 through 6 January 2016 ; Volume 1 , 2016 ; 9780791849651 (ISBN) Darbandi, M ; Sabouri, M ; Heat Transfer Division ; Sharif University of Technology
    American Society of Mechanical Engineers  2016
    Abstract
    We present the rarefaction effects on diffusive mass transport in micro- and nanoscales using the results of direct simulation Monte Carlo DSMC method. Unlike the previous investigations, the momentum and heat contributions are eliminated from the computations via uniform velocity, pressure, and temperature field considerations. The effects of global Knudsen number on the diffusion phenomenon are studied for the same Peclet number and a unique mixer shape. The results indicate that there is considerable weakening in diffusion mechanism for high Knudsen number cases. As a result, the non-dimensional diffusive mass fluxes would decrease and the non-dimensional mixing length would increase as... 

    Enhancement of surface adsorption-desorption rates in microarrays invoking surface charge heterogeneity

    , Article Sensors and Actuators, B: Chemical ; Volume 242 , 2017 , Pages 956-964 ; 09254005 (ISSN) Abdollahzadeh, M ; Saidi, M. S ; Sadeghi, A ; Sharif University of Technology
    Elsevier B.V  2017
    Abstract
    This investigation is devoted to the influences of non-uniform wall characteristics on the surface adsorption-desorption rates in an electrokinetic microarray. Utilizing already explored electroosmotic and electrophoretic velocities, the species transport equations are solved by a finite-volume-based numerical approach. Uniform, sinusoidal, and pulse-like distributions of the zeta potential are considered in the analysis. The developed model is validated by comparing the results with those of two analytical solutions that are derived for limiting conditions. The results reveal that, in some cases, the surface charge heterogeneity can reduce the saturation time by more than 60%. The efficacy... 

    Hydrodynamic dispersion by electroosmotic flow of viscoelastic fluids within a slit microchannel

    , Article Microfluidics and Nanofluidics ; Volume 22, Issue 1 , January , 2018 ; 16134982 (ISSN) Hoshyargar, V ; Talebi, M ; Ashrafizadeh, S. N ; Sadeghi, A ; Sharif University of Technology
    Springer Verlag  2018
    Abstract
    The biofluids being manipulated in lab-on-a-chip devices usually contain elastic macromolecules. Accordingly, for an accurate modeling of the relevant flow physics one should invoke viscoelastic constitutive equations. In this paper, attention is paid toward the hydrodynamic dispersion by the fully developed electroosmotic flow of PTT viscoelastic fluids in slit microchannels of low zeta potential. Adopting the Taylor–Aris approach, analytical solutions are derived for late-time solute concentration and effective dispersion coefficient. Finite element-based numerical simulations are also conducted to monitor the broadening of an analyte band from the moment of injection. Both approaches are... 

    Monte Carlo simulation of a lattice model for the dynamics of randomly branching double-folded ring polymers

    , Article Physical Review E ; Volume 104, Issue 1 , 2021 ; 24700045 (ISSN) Ghobadpour, E ; Kolb, M ; Ejtehadi, M. R ; Everaers, R ; Sharif University of Technology
    American Physical Society  2021
    Abstract
    Supercoiled DNA, crumpled interphase chromosomes, and topologically constrained ring polymers often adopt treelike, double-folded, randomly branching configurations. Here we study an elastic lattice model for tightly double-folded ring polymers, which allows for the spontaneous creation and deletion of side branches coupled to a diffusive mass transport, which is local both in space and on the connectivity graph of the tree. We use Monte Carlo simulations to study systems falling into three different universality classes: ideal double-folded rings without excluded volume interactions, self-avoiding double-folded rings, and double-folded rings in the melt state. The observed static properties... 

    An innovative three dimensional numerical model for bipolar plates to enhance the efficiency of PEM fuel cells

    , Article ASME 2012 10th International Conference on Fuel Cell Science, Engineering and Technology Collocated with the ASME 2012 6th International Conference on Energy Sustainability, FUELCELL 2012, 23 July 2012 through 26 July 2012 ; July , 2012 , Pages 351-360 ; 9780791844823 (ISBN) Arbabi, F ; Roshandel, R ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2012
    Abstract
    The efficiency of proton exchange membrane (PEM) fuel cell is straightly correlated to the bipolar plate design and fluid channel arrangements. Higher produced energy can be attained by optimal design of type, size, or patterns of the channels. Previous researches showed that the bipolar plate channel design has a considerable effect on reactant distribution uniformity as well as humidity control in PEM fuel cells. This paper concentrates on enhancements in the fuel cell performance by optimization of bipolar plate design and channels configurations. A numerical model of flow distribution based on Navier-Stokes equations using individual computer code is presented. The results gained from... 

    Transfer optimization in transit networks: Headway and departure time coordination

    , Article IEEE Conference on Intelligent Transportation Systems, Proceedings, ITSC ; 2011 , Pages 1531-1536 ; 9781457721984 (ISBN) Khani, A ; Shafahi, Y ; Sharif University of Technology
    Abstract
    This paper studies the scheduling problem in transit networks in order to decrease transfer waiting time. Transfer waiting time is calculated based on headway and departure time of intersecting routes and is divided into two parts. The first part can be reduced by changing departure times and was studied by the authors previously. The focus of the present research, however, is to minimize the second part of the transfer waiting time, dependent on the headways. The proposed optimization model in this paper includes both parts and is a nonlinear mathematical programming model. The model is decomposed to the departure time setting model (DSM) and the headway setting model (HSM). A solution... 

    Shear-rate-dependent rheology effects on mass transport and surface reactions in biomicrofluidic devices

    , Article AIChE Journal ; Volume 61, Issue 6 , 2015 , Pages 1912-1924 ; 00011541 (ISSN) Sadeghi, A ; Amini, Y ; Saidi, M. H ; Yavari, H ; Sharif University of Technology
    John Wiley and Sons Inc  2015
    Abstract
    Consideration is given to shear-rate-dependent rheology effects on mass transport in a heterogeneous microreactor of rectangular cross section, utilizing both numerical and analytical approaches. The carrier liquid obeys the power-law viscosity model and is actuated primarily by an electrokinetic pumping mechanism. It is discovered that, considering the shear-thinning biofluids to be Newtonian fluids gives rise to an overestimation of the saturation time. The degree of overestimation is higher in the presence of large Damkohler numbers and electric double layer thicknesses. It is also increased by the application of a favorable pressure gradient, whereas the opposite is true when an opposed... 

    A practical model for transfer optimization in a transit network: Model formulations and solutions

    , Article Transportation Research Part A: Policy and Practice ; Volume 44, Issue 6 , 2010 , Pages 377-389 ; 09658564 (ISSN) Shafahi, Y ; Khani, A ; Sharif University of Technology
    2010
    Abstract
    This paper studies the transit network scheduling problem and aims to minimize the waiting time at transfer stations. First, the problem is formulated as a mixed integer programming model that gives the departure times of vehicles in lines so that passengers can transfer between lines at transfer stations with minimum waiting times. Then, the model is expanded to a second model by considering the extra stopping time of vehicles at transfer stations as a new variable set. By calculating the optimal values for these variables, transfers can be better performed. The sizes of the models, compared with the existing models, are small enough that the models can be solved for small- and medium-sized... 

    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... 

    Numerical investigation on mixing intensification of ferrofluid and deionized water inside a microchannel using magnetic actuation generated by embedded microcoils for lab-on-chip systems

    , Article Chemical Engineering and Processing - Process Intensification ; Volume 147 , 2020 Saadat, M ; Shafii, M. B ; Ghassemi, M ; Sharif University of Technology
    Elsevier B.V  2020
    Abstract
    Effective and rapid mixing is crucial for chemical and biological processes. The purpose of the current study is to investigate the effect of steady and varying magnetic field on the mixing of a water-based ferrofluid and two streams of deionized water inside a microchannel for Lab-on-Chip applications. To this end, the nonlinear governing equations, the momentum equation, the continuity equation, the mass transport equation and the Maxwell-Ampere equations are numerically solved. A commercial code based on the finite-element method is used and the numerical simulations are validated by the experimental results in the literature. To augment the mixing performance, the effects of influencing...