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    Elastic Field of an Anticrack Via Reproducing Kernel Particle Method

    , M.Sc. Thesis Sharif University of Technology Sohrabpour, Amir Hossein (Author) ; Mohammadi Shodja, Hossein (Supervisor)
    Abstract
    Meshless Methods using kernel approximation like Reproducing Kernel Particle Method (RKPM) are methods for solving partial differential equations that require only nodal data and a description of the geometry without requiring element connectivity data and mesh producing. An innovative method of nonplanar material partitioning method (NMPM) with implementation of RKPM is employed to calculate the stress intensity factor (SIF) at the tip of an anticrack sited in an isotropic plate under a remote applied loading. Numerical examples in comparison with the exact closed form expressions show that accurate SIF for mode I can be obtained.

     

    Graph homomorphisms through random walks [electronic resource]

    , Article Journal of Graph Theory ; 2003, Volume 44, Issue 1, pages 15–38 Daneshgar, A. (Amir) ; Hajiabolhassan, Hossein ; Sharif University of Technology
    Abstract
    In this paper we introduce some general necessary conditions for the existence of graph homomorphisms, which hold in both directed and undirected cases. Our method is a combination of Diaconis and Saloff–Coste comparison technique for Markov chains and a generalization of Haemers interlacing theorem. As some applications, we obtain a necessary condition for the spanning subgraph problem, which also provides a generalization of a theorem of Mohar (1992) as a necessary condition for Hamiltonicity. In particular, in the case that the range is a Cayley graph or an edge-transitive graph, we obtain theorems with a corollary about the existence of homomorphisms to cycles. This, specially, provides... 

    Unique list-colourability and the fixing chromatic number of graphs [electronic resource]

    , Article Discrete Applied Mathematics ; Volume 152, Issues 1–3, 1 November 2005, Pages 123–138 Daneshgar, A. (Amir) ; Hajiabolhassan, Hossein ; Sharif University of Technology
    Abstract
    In this paper we introduce a chromatic parameter, called the fixing chromatic number, which is related to unique colourability of graphs, in the sense that it measures how one can embed the given graph G in G∪Kt by adding edges between G and Kt to make the whole graph uniquely t-colourable. We study some basic properties of this parameter as well as its relationships to some other well-known chromatic numbers as the acyclic chromatic number. We compute the fixing chromatic number of some graph products by applying a modified version of the exponential graph construction  

    Circular colouring and algebraic no-homomorphism theorems

    , Article European Journal of Combinatorics ; Volume 28, Issue 6, August 2007, Pages 1843–1853 Daneshgar, A. (Amir) ; Hajiabolhassan, Hossein ; Sharif University of Technology
    Abstract
    In this paper, we apply some new algebraic no-homomorphism theorems in conjunction with some new chromatic parameters to estimate the circular chromatic number of graphs. To show the applicability of the general results, as a couple of examples, we generalize a well known inequality for the fractional chromatic number of graphs and we also show that the circular chromatic number of the graph obtained from the Petersen graph by excluding one vertex is equal to 3. Also, we focus on the Johnson–Holroyd–Stahl conjecture about the circular chromatic number of Kneser graphs and we propose an approach to this conjecture. In this regard, we introduce a new related conjecture on Kneser graphs and we... 

    Density and power graphs in graph homomorphism problem

    , Article Discrete Mathematics ; Volume 308, Issue 17, 6 September 2008, Pages 4027–4030 Daneshgar, A. (Amir) ; Hajiabolhassan, Hossein ; Sharif University of Technology
    Abstract
    We introduce two necessary conditions for the existence of graph homomorphisms based on the concepts of density and power graph. As corollaries, we obtain a lower bound for the fractional chromatic number, and we set forward elementary proofs of the facts that the circular chromatic number of the Petersen graph is equal to three and the fact that the Coxeter graph is a core  

    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... 

    Arithmetic Theory of Quadratic forms with Several Variables

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Rasoul (Author) ; Jafari, Amir (Supervisor)
    Abstract
    In this thesis we review several arithmetical questions about the diophantine equation φ[x]=q where φ is a nondegenerate symmetric bilinear form on a finite dimensional vector space, φ[x] is the corresponding quadratic form and q is a nonzero element of the ground field. We obtain class number and mass formulae for the orthogonal group associated to φ in a number field utilizing the concept of quadratic forms, lattices and adelic language  

    Calculation of the Energy Release Rate of Nano-Cracks in FCC Materials Via the Many Body Atomic Scale FEM

    , M.Sc. Thesis Sharif University of Technology Ostad Hossein, Alireza (Author) ; Mohammadi Shodja, Hossein (Supervisor)
    Abstract
    Since the classical continuum theory fails to deal with the problems associated with defects, stress concentrators, and relevant deformation phenomena in solids, alternative approaches that can detect the atomistic nature of materials' fracture are required. The deficiency of the capture the size effect which yields delusively high values for some components of the stress field right on the edge of the stress concentrators, and its weakness in describing the complex interaction between small inhomogeneities, cracks and the like when they are only a few nanometers apart, are among some of the disadvantages of the classical approach. In recent years, however, atomistic methods are emerging to... 

    An Electromagnetism-Like Algorithm to Solve Three-Dimensional Highway Alignment Problem

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Ali (Author) ; Poorzahedy, Hossein (Supervisor)
    Abstract
    Road construction and maintenance constitute a significant part of country-wide infrastructure development budget each year. This indicates the importance of planning and design of individual road alignment in reducing the development cost. This study presents a meta-heuristic algorithm based on the concept of electromagnetism, which explores and finds a good route between two given points within a three-dimensional (3-D) context. It defines the region in a continuous 3-D surface, identifies initial routes, which are directed and shaped toward better positions by the help of local and global search. The final good solution is fine-tuned to produce a better alignment. The behaviour of the... 

    Optimal Command Control of Aircraft Anti-Skid Brake System

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Alireza (Author) ; Pourtakdoust, Hossein (Supervisor)
    Abstract
    The goal of this thesis is modeling and simulation of aircraft landing motion in order to evaluate the performance of an optimal anti-skid brake system (ABS) for the main landing gears with friction effects. In this process, the aircraft 6DOF perturbed equations of motion augmented with pertinent friction and brake forces and moments have been utilized. Subsequently, the problem is formulated within the framework of an optimal LQR that has allowed for generation of control brake commands as well as aircraft landing performance at different landing conditions with and without the proposed ABS. The results demonstrate the proposed ABS has been effective in providing admissible landing... 

    Pronunciation Scoring in Computer-Assisted Language Learning

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Sajede (Author) ; Sameti, Hossein (Supervisor)
    Abstract
    Due to the increase in the number of people interested in learning new languages, in recent years, multiple systems have been developed to teach new languages to those who are interested. These systems are called Computer Assisted Language Learning (CALL). However, the most credible CALL systems, like Duolingo, do not support Persian. So the of this study is to design and implement one of the technical parts of CALL systems, the Computer Assisted Pronunciation Training(CAPT), which is the part responsible for evaluating the learners' input voice's pronunciation and generating appropriate score and feedback.In this study, good pronunciation means correct expression of words, correct... 

    An STT-MRAM Cache Management Scheme for Retention Failure Reduction

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Abdollah (Author) ; Asadi, Hossein (Supervisor)
    Abstract
    Spin-Transfer Torque Magnetic RAM (STT-MRAM) is the most promising nonvolatile memory to replace SRAM technology in the Last-Level Cache (LLC) due to its benefits such as high density, near-zero cell leakage, and immunity to soft errors.However, due to its high retention failure and read disturbance rates in the downscaled technologies and the low data access rate in the LLC and the high number of read accesses, retention failure and read disturbance have become the main reliability challenges for STT-MRAM cache memory. The existing approaches to overcome these challenges impose significant area and performance overhead or adversely affect the other types of failures. In this thesis, we... 

    On the isoperimetric spectrum of graphs and its approximations [electronic resource]

    , Article Journal of Combinatorial Theory, Series B ; Volume 100, Issue 4, July 2010, Pages 390–412 Daneshgar, A. (Amir) ; Hajiabolhassan, Hossein ; Javadi, Ramin ; Sharif University of Technology
    Abstract
    In this paper1 we consider higher isoperimetric numbers of a (finite directed) graph. In this regard we focus on the nth mean isoperimetric constant of a directed graph as the minimum of the mean outgoing normalized flows from a given set of n disjoint subsets of the vertex set of the graph. We show that the second mean isoperimetric constant in this general setting, coincides with (the mean version of) the classical Cheeger constant of the graph, while for the rest of the spectrum we show that there is a fundamental difference between the nth isoperimetric constant and the number obtained by taking the minimum over all n-partitions. In this direction, we show that our definition is the... 

    Structural Health Monitoring Using Optimal Finite Element Model Based on Digital Image Correlation

    , M.Sc. Thesis Sharif University of Technology Amir Hossein Amir Ahmadi (Author) ; Khaloo, Alireza (Supervisor)
    Abstract
    The purpose of this research is to monitor the health of structures using the updated finite element model, in which digital images are used to optimize the numerical model. Structural Health Monitoring (SHM) is always an important and significant issue that has attracted the attention of many researchers in recent years. In general, some researches have been conducted in this field using physical sensors that provide discrete data to the system for analysis. Using cameras to monitor the structure makes it possible to extract continuous and integrated data from the structure using digital images, which is a significant advantage compared to physical sensors.In this research, a steel... 

    Multiple Zeta Values

    , M.Sc. Thesis Sharif University of Technology Mohammadi Zebarlu (Author) ; Jafari, Amir (Supervisor)

    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.... 

    The Effect of Radiation Pressure on Dust and Gas Dynamics in Accretion Disks

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Amir Hossein (Author) ; Rahvar, Sohrab (Supervisor)
    Abstract
    The purpose of this study is to investigate the effect of radiation pressure on accretion disks. The radiation density causes the separation of electrons from ions which leads to the creation of an internal electric dipole. In this study Radiation density is calculated using the Eddington limit. Afterwards radiation pressure is calculated with the use of collisions between photons and electrons in the plasma. Collisions are assumed to happen only between photons and electrons, due to the larger cross section of electrons compared to protons. The mentioned assumption causes the creation of an electric dipole and with it an internal electric field. The separation of the charges is assumed to... 

    Semisolid Stir Joining of As-Cast Silicon-Aluminum Bronze

    , M.Sc. Thesis Sharif University of Technology Ferasat, Keyvan (Author) ; Kokabi, Amir Hossein (Supervisor) ; Ashuri, Hossein (Supervisor)
    Abstract
    Aluminum Bronzes have many applications in marine environments. These alloys suffer from both hot cracking and cold cracking. In order to overcome the hot cracking and cold cracking, Semisolid Stir Joining method and a proper thermal cycle was used respectively. Effects of temperature, stirring rate, and tool type were investigated in Semisolid Stir joining method. In this method, butt joint design was used in order to place specimens, and the specimens were heated up to specific temperatures (920, 925, 930°C). A stirrer (Cylindrical and Grooved tool) with three rotational speeds (800, 1200, 1600 RPM) was introduced into the stir weld seam. Welded specimens were cooled to the 900°C... 

    Augmented RKPM Modeling of a Glide Edge Dislocation Near a Grain Boundary in the Framework of Surface/Interface Elasticity

    , M.Sc. Thesis Sharif University of Technology (Author) ; Mohammadi Shoja, Hossein (Supervisor)
    Abstract
    Traditional continuum theory of elasticity becomes remarkably inaccurate in the vicinity of singularities, and when the size eect is of concern. For example in the study of ultra-small objects and ultra-thin lms, near defects, near point of application of a concentrated load and as such, the classical solutions are not reliable. This work focuses on determination of the elastic elds of an edge dislocation near the grain boundary of two perfectly bonded nano-size crystals. It is proposed to study this problem in the context of surface/interface elasticity, and incorporate the eect of the grain boundary on the elastic elds. In contrast to the surface/interface elasticity theory, traditional... 

    Network Traffic Analyzer

    , M.Sc. Thesis Sharif University of Technology Silavi, Ehsan (Author) ; Jahangir, Amir Hossein (Supervisor)
    Abstract
    In order to increase the network performance, to discover network security threats, to guarantee the quality of services, to simulate networks and develop new network protocols, network designers and operators need software tools to analyze the network traffic. The first step to do this analysis is network monitoring. This can be done by using various software and hardware tools.
    In this research we developed a tool which analyzes the network traffic using appropriate statistical methods. The models which are analyzed in this application are: Poisson, Self-similar and Weibull. This application analyzes the network traffic based on this statistical models and calculates their parameters....