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    Investigation and Modeling of Polymer Electrolyte Membranes in PEM Fuel Cells

    , M.Sc. Thesis Sharif University of Technology Tavakoli Mehrabadi, Bahareh Alsadat (Author) ; Roshandel, Ramin (Supervisor)
    Abstract
    Fuel cells convert the chemical energy of hydrogen and oxygen directly into the electricity. Their high efficiency and low emissions have made them a prime candidate for powering the next generation electric vehicles. Polymer electrolyte membrane is a key component of the PEM fuel cells. One of the critical problems to overcome in some PEM fuel cells is the water management because If there is not enough water, the membrane becomes dehydrated which leads to a rapid increase in ohmic resistance. On the other hand, if too much water is present, flooding may occur resulting in the pores of the gas diffusion filled by water and the available passage for reactant gases is decreased. In this work... 

    Chromatic Sum in Graphs

    , Ph.D. Dissertation Sharif University of Technology Lotfalizadeh Mehrabadi, Mojtaba (Author) ; Mahmudian, Ebadolah (Supervisor)

    Preparation and Performance Assessment of Polymer-SAPO-34 Mixed Matrix Membrane for Separation of CO2 from Other Gases

    , M.Sc. Thesis Sharif University of Technology Meshkat Alsadat, Shadi (Author) ; Soltanieh, Mohammad (Supervisor) ; Mohammadi, Aliasghar (Supervisor)
    Abstract
    In this research incorporation of SAPO-34 zeolite filler into polycarbonate membrane was investigated for fabrication of mixed matrix membrane (MMM). The main purpose of addition of zeolite in polymer matrix is to enhance the separation properties of pure membrane by means of the selective pores of SAPO-34. SAPO-34 possesses pores with proper size for separation of CO2 from CH4 by molecular sieving mechanism. Pure polycarbonate membrane and PC/SAPO-34 MMM was prepared by solvent evaporation method using dichloromethane as solvent. Zeolite loading was varied between 5-30%wt. First of all, polycarbonate was characterized by DSC, FTIR and viscometer analysis in order to determine all the... 

    Actuator/sensor modeling for vibration of FGM solid circular plate using Reissner-Mindlin plate theory

    , Article ZAMM Zeitschrift fur Angewandte Mathematik und Mechanik ; Volume 90, Issue 4 , 2010 , Pages 287-308 ; 00442267 (ISSN) Jafari Mehrabadi, S ; Kargarnovin, M. H ; Najafizadeh, M. M ; Sharif University of Technology
    2010
    Abstract
    In this paper, the vibration of a constant thickness circular plate made of functionally graded material (FGM) is controlled by implementing two piezoelectric layers as a sensor and an actuator. Assuming that the material properties of FGM plate vary only in the thickness direction according to the power law manner, the governing differential equations are derived based on the Reissner-Mindlin plate theory (RMPT). Moreover, in a parallel work another set of differential equations are also derived using classical plate theory (CPT). Then for two different kinds of plate boundary conditions these coupled differential equations are solved using separation of variable technique and obtained... 

    Free vibration analysis of functionally graded coupled circular plate with piezoelectric layers

    , Article Journal of Mechanical Science and Technology ; Volume 23, Issue 8 , 2009 , Pages 2008-2021 ; 1738494X (ISSN) Mehrabadi, S. J ; Kargarnovin, M. H ; Najafizadeh, M. M ; Sharif University of Technology
    2009
    Abstract
    Based on classical plate theory (CLPT), free vibration analysis of a circular plate composed of functionally graded material (FGM) with its upper and lower surfaces bounded by two piezoelectric layers was performed. Assuming that the material properties vary in a power law manner within the thickness of the plate the governing differential equations are derived. The distribution of electric potential along the thickness direction in piezoelectric layers is considered to vary quadratically such that the Maxwell static electricity equation is satisfied. Then these equations are solved analytically for two different boundary conditions, namely clamped and simply supported edges. The validity of... 

    Model Based Testing in Software Product Line

    , M.Sc. Thesis Sharif University of Technology Zahiri Mehrabadi, Mahdieh (Author) ; Mirian-Hosseinabadi, Hassan (Supervisor)
    Abstract
    Software product line (SPL) engineering offers several advantages such as reduced costs, high quality and less time to market in development of family of software products. The goal of software product line is systematic and effective development of a set of software products which share common and managed set of features. Software product line testing has its special challenges such as scalability and variability, and has significant importance due to the importance of quality in software product line and enormous number of possible products. Most of the popular methods in this domain have shortcomings such as having seam between development and testing processes, limited application scope... 

    Gas permeation and sorption properties of poly(amide-12-b-ethyleneoxide)(Pebax1074)/SAPO-34 mixed matrix membrane for CO2/CH4 and CO2/N2 separation

    , Article Journal of Industrial and Engineering Chemistry ; Volume 27 , July , 2015 , Pages 223-239 ; 1226086X (ISSN) Rabiee, H ; Meshkat Alsadat, S ; Soltanieh, M ; Mousavi, S. A ; Ghadimi, A ; Sharif University of Technology
    Korean Society of Industrial Engineering Chemistry  2015
    Abstract
    Zeolite SAPO-34 was used for fabrication of mixed matrix membranes (MMMs) to improve the CO2/CH4/N2 gas separation performance of the neat Pebax1074 membrane. Permeability and selectivity of the MMMs were studied at different temperatures of 25-65°C and pressures of 4-24 bars. Also sorption of different gases in MMMs was measured at 35°C and different pressures, which showed enhanced solubility coefficients. Moreover, thermal, morphological and mechanical properties of MMMs were characterized by differential scanning calorimetry (DSC), scanning electron microscope (SEM) and tensile analysis. The results showed excellent improvement in... 

    Organic halides and nanocone plastic structures enhance the energy conversion efficiency and self-cleaning ability of colloidal quantum dot photovoltaic devices

    , Article Journal of Physical Chemistry C ; Volume 121, Issue 18 , 2017 , Pages 9757-9765 ; 19327447 (ISSN) Tavakoli, M. M ; Simchi, A ; Tavakoli, R ; Fan, Z ; Sharif University of Technology
    American Chemical Society  2017
    Abstract
    This paper presents solid-state ligand exchange of spin-coated colloidal lead sulfide quantum dot (PbS QD) films by methylammonium iodide (MAI) and integration of them in depleted heterojunction solar (DHS) devices having an antireflecting (AR) nanocone plastic structure. Time-resolved photoluminescence measurements determine a shorter lifetime of the charge carries on a semiconductor (TiO2) electron transfer layer for the MAI-passivated QD films as compared with those with long-chain aliphatic or short thiol ligands. Consequently, the DHS device yields improved power conversion efficiency (>125%) relative to oleic-acid-passivated PbS QD films. Using anodized aluminum oxide templates, an... 

    Surface engineering of TiO2 ETL for highly efficient and hysteresis-less planar perovskite solar cell (21.4%) with enhanced open-circuit voltage and stability

    , Article Advanced Energy Materials ; Volume 8, Issue 23 , 2018 ; 16146832 (ISSN) Tavakoli, M. M ; Yadav, P ; Tavakoli, R ; Kong, J ; Sharif University of Technology
    Wiley-VCH Verlag  2018
    Abstract
    Interfacial studies and band alignment engineering on the electron transport layer (ETL) play a key role for fabrication of high-performance perovskite solar cells (PSCs). Here, an amorphous layer of SnO2 (a-SnO2) between the TiO2 ETL and the perovskite absorber is inserted and the charge transport properties of the device are studied. The double-layer structure of TiO2 compact layer (c-TiO2) and a-SnO2 ETL leads to modification of interface energetics, resulting in improved charge collection and decreased carrier recombination in PSCs. The optimized device based on a-SnO2/c-TiO2 ETL shows a maximum power conversion efficiency (PCE) of 21.4% as compared to 19.33% for c-TiO2 based device.... 

    Efficient, hysteresis-free, and flexible inverted perovskite solar cells using all-vacuum processing.Efficient, hysteresis-free, and flexible inverted perovskite solar cells using all-vacuum processing

    , Article Solar RRL ; 2020 Tavakoli, M. M ; Yadav, P ; Prochowicz, D ; Tavakoli, R ; Sharif University of Technology
    Wiley-VCH Verlag  2020
    Abstract
    The fabrication of efficient perovskite solar cells (PSCs) using all-vacuum processing is still challenging due to the limitations in the vacuum deposition of the hole transporting layer (HTL). Herein, inverted PSCs using copper (II) phthalocyanine (CuPC) as an ideal alternative HTL for vacuum processing are fabricated. After proper optimization, a PSC with a power conversion efficiency (PCE) of 20.3% is achieved, which is much better than the PCEs (16.8%) of devices with solution-based CuPC. As it takes a long time to dissolve CuPC in the solution-based device, the evaporation approach has better advantage in terms of fast processing. In addition, the device with the evaporated CuPC HTL... 

    Efficient perovskite solar cells based on Cdse/Zns quantum dots electron transporting layer with superior UV stability

    , Article Physica Status Solidi - Rapid Research Letters ; Volume 14, Issue 6 , 2020 Tavakoli, M. M ; Prochowicz, D ; Yadav, P ; Tavakoli, R ; Sharif University of Technology
    Wiley-VCH Verlag  2020
    Abstract
    Stability is the main challenge in the field of perovskite solar cells (PSCs). Finding new strategies is required to protect the PSCs from deteriorating agents such as humidity, heating, and illumination. Herein, a new electron transporting layer (ETL), i.e., CdSe/ZnS quantum dots (QDs), is proposed for the fabrication of efficient and stable PSCs. CdSe/ZnS QDs layer not only works as an ETL but also has downshifting property, which can improve both efficiency and stability of the PSCs. Using CdSe/ZnS QDs ETL with green emission, a PSC with maximum power conversion efficiency (PCE) of 18% is achieved. More importantly, the device shows great UV stability, much better than the device with... 

    Multimaterial topology optimization by volume constrained Allen-Cahn system and regularized projected steepest descent method

    , Article Computer Methods in Applied Mechanics and Engineering ; Vol. 276 , 2014 , pp. 534-565 ; ISSN: 00457825 Tavakoli, R ; Sharif University of Technology
    2014
    Abstract
    A new computational algorithm is introduced in the present study to solve multimaterial topology optimization problems. It is based on the penalization of the objective functional by the multiphase volume constrained Ginzburg-Landau energy functional. The update procedure is based on the gradient flow of the objective functional by a fractional step projected steepest descent method. In the first step, the new design is found based on the projected steepest descent method to ensure the reduction in the objective functional, simultaneously satisfying the control constraints. In the second step, regularization step, an H1 regularity of the solution is ensured while keeping the feasibility of... 

    On the prediction of shrinkage defects by thermal criterion functions

    , Article International Journal of Advanced Manufacturing Technology ; Vol. 74, issue. 1-4 , Jun , 2014 , p. 569-579 Tavakoli, R ; Sharif University of Technology
    2014
    Abstract
    The goal of the present study is to predict the formation of solidification induced defects in castings by thermal criteria functions. In a criterion function method, the heat transfer equation is firstly solved, and then the susceptibility of defect formation at every point in the casting is predicted by computing a local function, criterion function, using results of the thermal analysis. In the first part of the paper, some famous criteria functions, in particular, the Pellini and Niyama criteria, are analyzed and their shortcomings are discussed in details. Then, a new criterion function is suggested to decrease the shape-dependency issue of the former criteria. The feasibility of the... 

    Computationally efficient approach for the minimization of volume constrained vector-valued Ginzburg-Landau energy functional

    , Article Journal of Computational Physics ; Volume 295 , August , 2015 , Pages 355-378 ; 00219991 (ISSN) Tavakoli, R ; Sharif University of Technology
    Academic Press Inc  2015
    Abstract
    The minimization of volume constrained vector-valued Ginzburg-Landau energy functional is considered in the present study. It has many applications in computational science and engineering, like the conservative phase separation in multiphase systems (such as the spinodal decomposition), phase coarsening in multiphase systems, color image segmentation and optimal space partitioning. A computationally efficient algorithm is presented to solve the space discretized form of the original optimization problem. The algorithm is based on the constrained nonmonotone L2 gradient flow of Ginzburg-Landau functional followed by a regularization step, which is resulted from the Tikhonov regularization... 

    Unconditionally energy stable time stepping scheme for Cahn-Morral equation: Application to multi-component spinodal decomposition and optimal space tiling

    , Article Journal of Computational Physics ; Volume 304 , 2016 , Pages 441-464 ; 00219991 (ISSN) Tavakoli, R ; Sharif University of Technology
    Academic Press Inc  2016
    Abstract
    An unconditionally energy stable time stepping scheme is introduced to solve Cahn-Morral-like equations in the present study. It is constructed based on the combination of David Eyre's time stepping scheme and Schur complement approach. Although the presented method is general and independent of the choice of homogeneous free energy density function term, logarithmic and polynomial energy functions are specifically considered in this paper. The method is applied to study the spinodal decomposition in multi-component systems and optimal space tiling problems. A penalization strategy is developed, in the case of later problem, to avoid trivial solutions. Extensive numerical experiments... 

    Optimal design of multiphase composites under elastodynamic loading

    , Article Computer Methods in Applied Mechanics and Engineering ; Volume 300 , 2016 , Pages 265-293 ; 00457825 (ISSN) Tavakoli, R ; Sharif University of Technology
    Elsevier  2016
    Abstract
    An algorithm is proposed to optimize the performance of multiphase structures (composites) under elastodynamic loading conditions. The goal is to determine the distribution of material in the structure such that the time-averaged total stored energy of structure is minimized. A penalization strategy is suggested to avoid the checkerboard instability, simultaneously to generate near 0-1 topologies. As a result of this strategy, the solutions of presented algorithm are sufficiently smooth and possess the regularity of H1 function space. A simple method for the continuum adjoint sensitivity analysis of the corresponding PDE-constrained optimization problem is presented. It is general and can be... 

    On the coupled continuous knapsack problems: projection onto the volume constrained Gibbs N-simplex

    , Article Optimization Letters ; Volume 10, Issue 1 , 2016 , Pages 137-158 ; 18624472 (ISSN) Tavakoli, R ; Sharif University of Technology
    Springer Verlag  2016
    Abstract
    Coupled continuous quadratic knapsack problems (CCK) are introduced in the present study. The solution of a CCK problem is equivalent to the projection of an arbitrary point onto the volume constrained Gibbs N-simplex, which has a wide range of applications in computational science and engineering. Three algorithms have been developed in the present study to solve large scale CCK problems. According to the numerical experiments of this study, the computational costs of presented algorithms scale linearly with the problem size, when it is sufficiently large. Moreover, they show competitive or even superior computational performance compared to the advanced QP solvers. The ease of... 

    Thermal optimization of the continuous casting process using distributed parameter identification approach—controlling the curvature of solid-liquid interface

    , Article International Journal of Advanced Manufacturing Technology ; Volume 94, Issue 1-4 , 2018 , Pages 1101-1118 ; 02683768 (ISSN) Tavakoli, R ; Sharif University of Technology
    Springer London  2018
    Abstract
    Thermal optimization of the vertical continuous casting process is considered in the present study. The goal is to find the optimal distribution of the temperature and interfacial heat transfer coefficients corresponding to the primary and secondary cooling systems, in addition to the pulling speed, such that the solidification along the main axis of strand approaches to the unidirectional solidification mode. Unlike many thermal optimization of phase change problems in which the desirable (target) temperature, temperature gradient, or interface position are assumed to be a priori known, a desirable shape feature of the freezing interface (not its explicit position) is assumed to be known in... 

    Smooth modeling of solidification based on the latent heat evolution approach

    , Article International Journal of Advanced Manufacturing Technology ; Volume 88, Issue 9-12 , 2017 , Pages 3041-3052 ; 02683768 (ISSN) Tavakoli, R ; Sharif University of Technology
    Springer London  2017
    Abstract
    The regularity problem of heat conduction equation corresponding to modeling of solidification based on the latent heat evolution approach is considered in the present study. It is shown that the corresponding PDE is actually semi-smooth, an issue that has not been taken into account explicitly in the related literature. A general smoothing (regularization) strategy is introduced to solve this problem. More specifically, the smoothed version of the effective heat capacity method is presented in this work. The presented approach is applied to model the quasi steady-state heat transfer problem in the continuous casting process. Numerical experiments demonstrate the success of the presented... 

    CartGen: Robust, efficient and easy to implement uniform/octree/embedded boundary Cartesian grid generator

    , Article International Journal for Numerical Methods in Fluids ; Volume 57, Issue 12 , 30 August , 2008 , Pages 1753-1770 ; 02712091 (ISSN) Tavakoli, R ; Sharif University of Technology
    2008
    Abstract
    An efficient and easy to implement method to generate Cartesian grids is presented. The presented method generates various kinds of Cartesian grids such as uniform, octree and embedded boundary grids. It supports the variation of grid size along each spatial direction as well as anisotropic and non-graded refinements. The efficiency and ease of implementation are the main benefits of the presented method in contrast to the alternative methods. Regarding octree grid generation, applying a simple and efficient data compression method permits to store all grid levels without considerable memory overhead. The presented method generates octree grids up to a 13-level refinement (81923 grids on the...