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    On the Effects of Change in the Ownership of Natural Resource Revenues on Government Performance Enhancement and People Welfare

    , M.Sc. Thesis Sharif University of Technology Mohsenzadeh Kermani, Amir Reza (Author) ; Nili, Masoud (Supervisor)
    Abstract
    The poor economic performance of natural resource abundant countries has been studied for a long time and in order to alleviate this problem some different solutions are suggested by economists. One stream among these solutions are those focusing on the distribution mechanism of natural resource revenues and the ownership of these resources. In this study, it is intended to address the effect of change in the ownership of natural resources on politicians’ behavior and people welfare by using political economy approach. Also the optimal share of people from natural resources as a function of political and economic institutions is discussed. In this study, it is shown theoretically that under... 

    Essays on Urban and Housing Economics

    , Ph.D. Dissertation Sharif University of Technology Tajrishy, Mohammad Saeed (Author) ; Vesal, Mohammad (Supervisor) ; Mohsenzadeh Kermani, Amir (Supervisor)
    Abstract
    The challenges of urbanization have been the focus of researchers since the past. With the expansion of urbanization and massive migration of people from villages to cities, these challenges became more important in our country. These issues, which exist in many other countries in a serious manner, are discussed in the branch of urban economy in the world. This thesis is arranged in three chapters, in each of which one of the aspects related to urban economy and housing is discussed. In the first chapter, the effects of the construction of Mehr housing on the value of nearby residential properties are investigated using difference-in-difference method. It is shown that the construction of... 

    On small uniquely vertex-colourable graphs and Xu's conjecture [electronic resource]

    , Article Discrete Mathematics ; Volume 223, Issues 1–3, 28 August 2000, Pages 93–108 Daneshgar, A. (Amir) ; Naserasr, Reza ; Sharif University of Technology
    Abstract
    Consider the parameter Λ(G) = |E(G)| - |V(G)|(k - 1) + (k2) for a k-chromatic graph G, on the set of vertices V(G) and with the set of edges E(G). It is known that Λ(G)≥0 for any k-chromatic uniquely vertex-colourable graph G (k-UCG), and, S.J. Xu has conjectured that for any k-UCG, G, Λ(G) = 0 implies that cl(G) = k; in which cl(G) is the clique number of G. In this paper, first, we introduce the concept of the core of a k-UCG as an induced subgraph without any colour-class of size one, and without any vertex of degree k - 1. Considering (k, n)-cores as k-UCGs on n vertices, we show that edge-minimal (k, 2k)-cores do not exist when k ≥ 3, which shows that for any edge-minimal k-UCG on 2k... 

    Fabrication of Bioactive Bone Cement

    , M.Sc. Thesis Sharif University of Technology Mansoori Kermani, Amir Reza (Author) ; Bahrevari, Mohammad Reza (Supervisor) ; Mashayekhan, Shohreh (Supervisor) ; Abd Khodaei, Mohammad Jafar (Supervisor)
    Abstract
    PMMA bone cement lacks biodegradability and the ability to bond with surrounding bone tissue. Therefore, the development of a new generation of bioactive bone cements that are biodegradable and possess adequate mechanical properties as well as desirable setting time is receiving remarkable interest.In this study, we have developed novel mineral-based bioactive bone cements. Our mineral bioactive bone cements were composed of Calcium Sulfate Hemihydrate, Bioactive Glass, and Tricalcium Silicate. Firstly, a binary system composed of Calcium Sulfate Hemihydrate and Bioactive Glass was optimized based on mechanical and setting behavior. Secondly, Tricalcium Silicate was added to the powder phase... 

    Crack Propagation Modeling in Arched Concrete Structures Reinforced by FRP Using XFEM and Damage Model

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Amir Hossein (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    In practice, structures made of concrete are full of cracks. The strength of concrete is mainly determined by the tensile strength, which is about 10% of the compressive strength. As long as cracking in concrete is unavoidable, we have to try to minimize their detrimental effects. This objective can be achieved by resisting (or limiting) propagation of existing cracks. Because of this, reinforcement (mostly steel) is used to increase the carrying capacity of the material and to control the development of cracks. Concrete structures that fail, already shows a large number of large and small cracks before their maximum carrying capacity is reached. The failure of concrete can be characterized... 

    Investigation of the Photonic Scattering Error in Radiography of Pipes and its Evaluation by Mote- carlo Simulation

    , M.Sc. Thesis Sharif University of Technology Masoumi Kolvanaq, Hojjat (Author) ; Vossoughi, Nasser (Supervisor) ; Movafeghi, Amir (Co-Advisor) ; Kermani, Abotaleb (Co-Advisor)
    Abstract
    Non-destructive testing method is for detect specimen flaws such as (crack, porosity, impure, welding defects, corrosion etc.) without destruction the specimen under inspection. Particular characteristic of radiography is an image product from specimen inside under testing where help to identity and better comprehend at flaw nature. Photon scattering is one of important factor to reduce image quality and signal to noise ratio. Scattered photons can due toexistent ingredient in the radiography environment and curvature of material transmission pipe where cause the disorder creation in the radiography images. In this research, pipe radiography simulated using the TIC and TIR radiography... 

    A Thermo-Mechanical Multi-Scale Simulation for the Compaction Process of the Oxide-Coated Aluminum Nano-Powders

    , M.Sc. Thesis Sharif University of Technology Orvati Movaffagh, Amir Mohammad (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    This research introduces a novel thermo-mechanical multiscale technique, utilizing machine learning, for simulating the compaction process of aluminum nanopowders with surface oxidation at various temperatures. The methodology employed involves the utilization of nonlinear thermo-mechanical Finite Element Method (FEM) for macro scale analysis, while employing the Molecular Dynamics (MD) method to calculate the mechanical and thermal characteristics of aluminum nanopowders at the nano-scale. The first part of the research presents a comprehensive study on the thermal conductivity of alumina-coated aluminum nanopowders, which is a crucial property for their application in powder metallurgy,... 

    Polygonal Finite Element Modeling of Fracture Mechanism and Crack Propagation

    , M.Sc. Thesis Sharif University of Technology Yasbolaghi, Reza (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    Fracture is one of the most important engineering problems, and the lack of knowledge about this phenomenon will result in loss of life and property. Before the computer age, fracture mechanics has been studied by many analytical mechanics researchers; and after that, lots of attempts have been done to accurately model this phenomenon.
    Finite element method, one of the best methods in Computational Mechanics, is common in computational fracture mechanics. Polygonal finite element is a new concept which has been recently applied in finite element analysis. This research utilized this concept in com-putational fracture mechanics. In another word, the crack discontinuity and crack tip... 

    XFEM Modeling of Dynamic Cohesive Crack Propagation in Saturated Porous Media

    , M.Sc. Thesis Sharif University of Technology Babazadeh, Mohsen (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    In this thesis, a fully coupled numerical model is developed for the modeling of dynamic cohesive crack propagation and hydraulic fracture in saturated porous media using extended finite element method. Many engineering structures like concrete or soil dams and buildings foundation are built with porous materials like concrete, rock and soil. Behavior of these materials in which void among the solid particles are filled with one or more fluids are so complicated rather than single solid phase. Dynamic analysis of porous mediums containing a discontinuity has many applications in various civil engineering fields including structure, earthquake, hydraulic structures, etc. For instance... 

    Multi-sclae Modeling for Determination of Thermal Properties of Silicon Nanostructures Via Molecular Dynamics (MD) and Finite Element Method (FEM)

    , Ph.D. Dissertation Sharif University of Technology DorMohammadi, Hossein (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    The band gap offset is an effect of coordination numbers (CNs) of atoms reduction at the edge of transversal cross-section Si nanowires (SiNWs) which would be of increasingly important for greater shell-core ratio sections. In this paper, a hierarchical multi-scale modeling has been developed to simulate edge effect on the band gap shift of SiNWs due to geometry effect induced strain in the self-equilibrium state. Classical Molecular Dynamics (MD) approach and Finite Element Method (FEM) are used in the micro (atomic) and macro scale levels, respectively. Using the Cauchy-Born (CB) hypothesis as a correlator of continuum and atomic properties, the atomic positions are related to the... 

    Multiscale Modelling the Nonlinear Behavior of Metallic Nano-powder Compaction Process

    , M.Sc. Thesis Sharif University of Technology Mofatteh, Hossein (Author) ; Khoie, Amir Reza (Supervisor)
    Abstract
    In present research forming process of nanopowders, which is a part of powder metallurgy was investigated by molecular dynamics method. Powder metallurgy is a relatively new method for production of industrial parts by pouring powder into die and compaction to desired density. One can reach parts with higher quality and strength by decreasing size of powder’s particles and entering the nano scale. Particle with smaller size have higher specific surface and due more intensity to react. Classic methods for investigation of this process don’t cover the atomic scale effects, so using newer procedures such as molecular dynamics is highly recommended. In present research, at first compaction of... 

    Coarse-gained Multi-scale Modeling for Numerical Simulation of Nonlinear Behavior of Materials in Nano-scale

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Khashayar (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    In this thesis, a coarse-grained multi-scale method for 2D crystallyn solids based-on finite element consepts has presented. In this method, both scales are atomic scale and similar to what we see in non-local QC method, the entire atomic structure will be intact. Accordingly, calculations of potential functions and forces in the domain will have the atomic accuracy. In the presented method to reduce the domain’s degrees of freedom, the classical finite-element meshing concept to mesh the elastic linear areas in the domain is used and the MD calculations will done on the mesh nodes. Therefore, degrees of freedom in the system will reduce and consequently, the computational cost will reduce.... 

    Modeling the Dynamic Contact with Large Deformations Using the G-ALE-FEM Method

    , M.Sc. Thesis Sharif University of Technology Mohajeri, Sina (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    Contact between different parts of a system and their interactions on each other is one of the most important phenomena that we face in modeling a variety of mechanical issues which should be carefully considered. Sometimes, this phenomenon occurs between different components in a phase and some other times between several phases, which, causes changes in the performance and response of the system. Therefore, in order to investigate its effect in particular on dynamic problems that are subject to severe changes over a short period of time, and to provide more effective methods for dealing with it, the subject of this research has been devoted to dynamic contact modeling with large... 

    The effect of tricalcium silicate incorporation on bioactivity, injectability, and mechanical properties of calcium sulfate/bioactive glass bone cement

    , Article Ceramics International ; Volume 49, Issue 10 , 2023 , Pages 15003-15014 ; 02728842 (ISSN) Mansoori Kermani, A ; Mashayekhan, S ; Kermani, F ; Abdekhodaie, M. J ; Sharif University of Technology
    Elsevier Ltd  2023
    Abstract
    The conventional Polymethyl methacrylate (PMMA) bone cement is not biodegradable and not bioactive to bond with the native bone and causes tissue necrosis resulting from its high exothermic polymerization. Hence, biodegradable bioactive bone cements with suitable setting time and mechanical properties should be introduced. In this study, novel bioactive bone cements containing Calcium Sulfate Hemihydrate (CSH), Bioactive Glass (BG), and Tricalcium Silicate (TSC) were developed. Firstly, CSH and BG binary system was optimized based on preliminary setting and mechanical tests. Secondly, the composite bioactive bone cements were obtained by adding different quantities of TCS to the optimized... 

    Modeling of Incompressible Materials Using the Extended Finite Element Method (XFEM)

    , M.Sc. Thesis Sharif University of Technology Mirkhosravi, Poorya (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    In the limit case of incompressibility, the displacement-based finite element methods are not capable of finding the solutions with adequate accuracy. Moreover, discontinuities in displacement field or strain field which exist in the interior of the elements should be dealt with appropriately. The u/p mixed formulation provides a suitable context for modeling the incompressible problems. It is capable of solving general problems in which there exist geometrical or material nonlinearities. In the case of employing the eXtended Finite Element Method (XFEM), uniform meshes can be used for problems with discontinuities and in fact the discontinuities can be decoupled from the mesh. In this... 

    Application of Isogeometric Method in Modeling and Analyzing Crack Growth Problems

    , M.Sc. Thesis Sharif University of Technology Esmaeili, Mir Sardar (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    Isogeometric Analysis method is a newly introduced method for the analysis of problems governed by partial differential equations. The method has some features in common with the finite element method and some in common with the mesh-less methods. This method uses the Non-Uniform Rational B-Splines (NURBS) functions as basis function for analysis. With this basis functions, the refinement procedure is much easier than the classical finite element method by eliminating the need to communicate with the CAD model. Modeling cracks in classical finite element method requires very fine mesh near the crack tip. One can model crack propagation by means of classical finite element, using an updating... 

    Modeling of Crack Propagation in Non-isothermalsaturatedPorous Media using XFEM

    , M.Sc. Thesis Sharif University of Technology Moallemi, Sina (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    The probability of crack appearance in soil structures and porous media is not avoidable, which could be the reason of structures collapse. According to the important affects, which they play in the vulnerability of the structures, they should be taking into account. The cracks have different effects on various materials. The most properties that cracks have, is their ability of conveying the fluid flow. For the most accurate analysis of discontinues domains, their governing equations should be taken and solved. Finite Element Method is one of the best solutions of differential governing equations. However, the appearance of some problems in the modeling of discontinues domain, was the... 

    Simulation of Crack Propagation in Ductile Metals Under Dynamic Cyclic Loading by Adaptive Finite Element Method and Continuum Damage Mechanics Model

    , M.Sc. Thesis Sharif University of Technology Eghbalian, Mahdad (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    Crack nucleation and growth is unfavorable in many industrial and every day-life cases. designers’ effort is to prevent or delay it by taking into account safety and maintenance considerations; but in some industrial operations, the main target is to form a crack in a part to achieve a particular shape; and designers’ duty is to control the way it happens. so numerical modeling of this phenomena has many useful applications in preventing the structures’ failure and designing the production processes for industrial goods; and because of this, a great attention has been paid to it in the last two decades. a situation usually encountered in every day-life is the earthquake excitation which... 

    Three-Dimensional Cohesive Modeling of Curved Crack Growth in Quasi-brittle Material Using Adaptive Technique

    , M.Sc. Thesis Sharif University of Technology Sharifi, Mahdi (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    Prediction of crack growth is one of the greatest achievements of continuum mechanics in 20th century. However, in spite of Griffith’s achievements, nowadays lots of subjects remain unchallenged in the field of Fracture Mechanics. Concrete and asphalt concrete are two of the most popular material in civil engineering and crack growth prediction in these materials are very important. Cohesive crack model is one of the models which is used for prediction of crack growth in quasi-brittle material such as concrete and it has been used widely in recent years because of simplicity and good agreement with experiment.The aim of this thesis is three-dimensional static and dynamic cohesive modeling of... 

    Modeling of Crack Propagation in Saturated Two Phase Porous Media Using X-FEM

    , M.Sc. Thesis Sharif University of Technology Vahhab, Mohammad (Author) ; Khoei, Amir Reza (Supervisor)
    Abstract
    Twophase medias are one of the most complicated medias in engineering and because of its importance, its been considered by a lot of researchers ever since. Varaioty of the problems in these medias, has ended in lots of methods for studing them. The primariative efforts in modeling deformable pouros medias was done by Terzaghi and others have improved the primary consepts and have suggested different methods. One of the most common and applicable methods in these medias is u-p formulation. This form is applicable in low frequencies (such as earthquakes) with great accuracy. In this thises, this form is used as primery formulation. Because deformation in multiphase problems can be large, in...