Sharif Digital Repository

Graph Theory and Combinatorial Analysis like the other branches of science use the probability for solving their problems. At the first , we will introduce the most common tools from probability used in Discrete Mathematics, such as “The Lovasz Local Lemma”. Most of them are based on Linearity of Expectation, Concentration Theorems and some other innovative methods such as Deletation Method. We will present different examples for these techniques. Also we will introduce “Random Graphs” and their importance. Specially we will explain how to use “Threshold Functions” to obtain different properties about the majority of graphs. Rainbow Connection, is a natural and interesting quantifiable way... 

This thesis is concerned with a fundamental problem in computational geometry. This problem inspects covering a space with a set of points provided that each point of the space is visible to at least one point from the selected subset. Applications of these problems are in the areas such as geographic information systems (GIS), robotics,computer graphics and the military.The investigated space is a planar rectangular region which is partitioned into smaller rectangles by connected edges. The objective of this study is to find an optimized corridor; i.e., a connected subset of edges which contains at least one point from each rectangle. For the minimum diameter corridor problem, an exact... 

Stochastic Algebraic Topology studies stochastic or less known spaces that depend on many random variables from the perspective of algebra. Examples of such spaces included random graphs of Erdos and Renyi and random simplicial spaces of higher dimension . In this thesis , we study algebraic aspects of these spaces such as homotopy groups and homology groups from probabilistic point of view , when the number of vertices of these spaces tend to infinity . The study of these spaces have a lot of applications, since the data for a given space can be incomplete . They are also used in big system structures. We have given a collection of new results in stochastic algebraic topology of two... 

On average there are to resistance spot welding connections per vehicle. The quality of these welding directly affects the quality of the finished product and the strength of the vehicle against various loads, including road roughness, different maneuvers and even sudden impacts from accidents. During the spot welding process, unintentional failures occur due to the wrong choice of current, force and time. The aim of this study is to investigate the fatigue strength of three-sheets welding joints in numerical and laboratory methods, considering the defects of (Undersize weld, Stick, edge of sheet metal and Edge of sheet metal-SECANT) . For this purpose, a healthy spot welding model was first... 

In recent years use of concrete filled steel tube column structures has been increased due to their several advantages. In these columns the steel tube provides confinement for the concrete core of the column, so it increases axial strength and flexibility of the concrete core, and prevents spalling of the concrete. On the other hand the concrete core delays the local buckling steel tube and increases its bearing capacity. In addition, these columns have higher stiffness and strength than typical concrete columns due to placement of steel in farthest point of column cross section. The steel tube besides its structural role acts as framework for the concrete core and reduces time and cost of... 

Double angle connections, which are welded to the beam web and bolted to the column flange, are usually used to make hinged or semi-hinged connections. Several models are presented in this study whose geometrical properties are different. The finite element software package is used to develop the finite element analysis of the connections. An analytical method is presented that can be used to determine the behavior and deformation for this type of connection. The correctness of Moment-rotation curves of finite element analysis for each connection has been ascertained by comparison, using analytical technique; and a very good agreement has been obtained  

This study considers blood flow in total cavopulmonary connection (TCPC) morphology, which is created in Fontan surgical procedure in patients with single ventricle heart disease. Ordinary process of TCPC operation reduces the pulmonary blood flow pulsatility; because of right ventricle being bypassed. This phenomenon causes a lot of side effects for patients. A cardiac surgeon has suggested that keeping main pulmonary artery (MPA) partially open, would increase pulmonary flow pulsations. MPA gets closed in ordinary TCPC operation. The purpose of current study is to verify the effects of keeping MPA partially open on pulmonary flow pulsations, by means of computational fluid dynamics (CFD).... 

In this thesis, coordination of a group of autonomous agents, through a scalable control structure and with very limited communications, is addressed. Inter-agent action functions are designed to guarantee the network connectivity. Two coordinator agents with different natures are designed. One is attractive and is named leader-agent (LA). The other is repulsive and is named shepherd-agent (SA). Under the assumption that both coordinators locally affect the group, we have proved that the governing equation of the whole group may have variable order.
By using nonlinear control techniques, coordination algorithms are designed to move the group on a predefined path or to a destination. It... 

In this study Donepezil effect on the brain functional connectivity investigated. In order to construct the brain functional network, EEG artifacts must firstly be removed because this step has important effects on the final interpretation of the results. Therefor, a new artifact removing method is proposed and better performance of the proposed method compared to other existing methods is stated using quantitative evaluations. After artifact removal, the functional brain network is extracted using conventional methods that were applied in the similar previous studies. The reasons for using conventional methods are their simplicity and reliability. Furtheremore, to study the recent... 

The functional network of the human brain is altered in many neurological and psychiatric disorders. Characterizing brain activity in terms of functionally segregated regions does not reveal anything about the communication among different brain regions and how such inter-communication could influence neural activity in each local region. The aim of this project is to assess the functional connectivity from resting state functional magnetic resonance imaging (fMRI) data. Spectral clustering algorithm was applied to the simulated, realistic and real fMRI data acquired from a resting healthy subject to find functionally connected brain regions. In order to make computation of the spectral... 

Autism spectrum disorders (ASD) have been defined as developmental disorders characterized by abnormalities in social interaction, communication skills, and behavioral flexibility. Over the past decades, studies using various genetic, neurobiological, cognitive and behavioral approaches have sought a single explanation for the heterogeneous manifestations of ASD, but no consensus on the etiology of ASD has emerged. Further studies aim to clarify the mechanism of disease.
Functional Magnetic Resonance Imaging (fMRI) is a new way of imaging which evaluates activity of brain by measuring magnetic difference caused by oscillation in blood oxygen level. fMRI has been widely used in recent... 

The spectrum of a graph is related to many important combinatorial parameters. Let (G), ′(G) be the maximum number of edge-disjoint spanning trees and edge-connectivity of a graph G,respectively. Motivated by a question of Seymour on the relationship between eigenvalues of a graph G and bounds of (G), we use eigenvalue interlacing for quotient matrix associated to graph to get the relationship between eigenvalues of a graph and bounds of (G) and ′(G). We also study the relationship between eigenvalues and bounds of (G) and ′(G) in a multigraph G. In the first chapter we prove eigenvalue interlacing and give several applications of it for obtaining bounds for characteristic numbers of... 

In order to ensure the safety of the plants, a set of commissioning tests based on international standards for nuclear power plants is carried out before operation. In this research, one of the Bushehr power plant commissioning tests, the loop connection primary circuit cooling pump test, was simulated using the RELAP5 code. In this test, the effects of loop connection primary circuit pumps on the thermohydraulic parameters and the eneterance of test-related systems was evaluated. After simulating the systems related to the test and extracting the results of the stable state, were evaluated the transient results was obtained with the experimental results of the test of loop connection the... 

Development of the fMRI imaging method gives the scientists the opportunity to record functional images from the brain with high spatial resolution and several researches were conducted on this field. Autistic people’s brain has functional differences with normal people. In this paper these differences have been studied. At first fMRI datasets from autistic subjects and control have been recorded and preprocessed. Then the independent components from these datasets have been extracted using group ICA method. Any independent component is an image depicting a brain network. There is a time series for each image which shows the temporal variations of each component. In the next step, the... 

In this thesis we study Manin’s proof of Mordel conjecture for function fields in characteristic 0 and restate it using modern algebraic geometry language. First we define an important tool for study of geometry of varieties over function fields: Gauss-Manin connection. Then we study Picard-Fuchs equations as a tool for translating geometric information about variety to arithmetic information. Finally we study height functions over function fields and their relations with Picard-Fuchs equations  

Block shear failure in the parent material is considered as a common potential failure mode in welded connections used in steel structures. However, there is only little research reported on the block shear failure of welded connections under multiaxial loading. Multiaxial loading is defined as loading not parallel or perpendicular to weld lines and in the case of in planar eccentricity results in torsional loads. In this research a nonlinear finite element model is developed to study the effect of connection geometry, weld group configuration, and eccentricity of lap splice connection on block shear capacity. The case studied concerns a 3 milimeter thick structural steel plate (CSA G40.21... 

One of the critical challenges in droplet based micro- and nanofluidic devices is handling the droplet breakup such that a controllable droplet size is produced. The experimental and numerical investigations at the microscale indicate that the droplet size can be well controlled by T junction geometries. In the present study we use non-equilibrium molecular dynamics (NEMD) simulations to investigate this phenomenon at the nanoscale. In order to generalize the study the Lennard-Jones type potential between the fluids and the walls have been considered and the strength and the effective range of the potential are changed to consider a wide variety of materials. Our results reveal that the... 

In recent decades, restoring residual deformations and adding the capability of returning to initial deformed state was investigated by many researchers. Steel Plate Shear Wall (SPSW) is one of structural earthquake resisting system that have high ductility capacity and good energy absorption property. On of major issues in SPSW systems is intense nonlinear deformation in panel’s infill web plate and this panels vertical and horizontal boundary elements. By incorporating Shape Memory Alloy (SMA) connections we can add returning to first deformed condition (self-centering) and sustain high ductility capacity to many structures. In this research the addition of SMA connections to SPSW system... 

A special steel beam-to-column connection, named Khor-jini, is commonly used for steel framing system in Iran. In this system, two continuous beams are passed next to the columns and are connected to the column side using seated brackets.This type of connection has been common in Iran from the late past. Unfortunately, the seismic behavior of Khorjini frames had not been sufficiently studied prior to Manjil Earthquake of 1990. Due to very large damages which occurred in steel structures especially in connections during the said earthquake, the seismic behavior of this type of connection was studied and some of its weak points were recognized.In this study non-linear... 

The purpose of this research is to study the behavior of conventional and retrofitted Khorjini connections. Thus the software ABAQUS 6.11 was used to fabricate the FEM models of the connections with experimental prototypes. In analytical studies, 21 specimens with different size of the connection components were analyzed. True stress–strain curves for steel and weld materials were used and damage initiation and revolution were considered in the weld material. Also cracking of the welds were considered by a micromechanical method. Behavioral characteristics of the conventional connections are specified and appropriate relations are suggested, using Stability equations of the connection...