Sharif Digital Repository

corrosion of steel reinforcements in concrete is one of the most important reasons for durability reduction of offshore structures. To reduce the diffusion rate of ion reactivity in concrete and its reinforcement surface, different methods such as chemical change and coating of reinforcement and concrete are used. In this research for increase corrosion resistance, effect of Pozzolanic additive materials such as fly ash and micro silica , in optimized percentages, 25% and 10% by weight of cement respectively, the percentage of polypropylene fibers improved 2.5% volume of concrete and Ferrogard-901 industrial inhibitor with 3% by weight of cement in concrete mixing plan, were investigated.... 

We study colorings of quasiordered sets (qosets) with a least element 0. To any qoset Q with 0 we assign a graph (called a zerodivisor graph) whose vertices are labelled by the elements of Q with two vertices x; y adjacent if the only elements lying below x and y are those lying below 0. We prove that for such graphs, the chromatic number and the clique number coincide  

Let (P;≼) be a partially ordered set (poset, briefly) with a least element 0. In this thesis, we deal with zero-divisor graphs of posets. We show that if the chromatic number r(P) and the clique number r(P) (x(r(P)) and !(r(P)), respectively) are finite, then x(r(P)) = !(w(P)) = n in which n is the number of minimal prime ideals of P. We also prove that the diameter of such a graph is either 1, 2 or 3 while its girth is either 3, 4 or 1  

Conflict-free coloring problem is one of the computational geometry problems that has been studied in the last two decades. The root of this problem comes from the frequency assignment to cellular networks problem. In that research, we have a cellular network containing several regions in two-dimensional plane and we want to assign a frequency to each of the regions so that if we look at any intersection of them, there is a region with a unique color compared to other regions of that intersection. In other words, a person’s cellular phone in the range of some regions (in the intersection of them) would be able to connect to one antenna with a unique frequency and function properly. This... 

There is much interest in the theoretical study of the structure of hypercubes because their structure has played an important role in the development of parallel processing and is still quite popular and influential.This thesis will begin with an introduction to hypercubes and some of their problems. Then we study the following concepts: Arboricity (The minimum number of edge-disjoint forests into which a graph can be decomposed), Galactic number (similar to arboricity but such that each component of each forest is a star), Silver coloring (Given a set I of maximal independent vertices, a silver coloring with respect to I is such that every v 2 I sees every other colors in its closed... 

Problem of 2-colorability of hypergraphs was introduced by Erd?os in 1963, and there are many results about this problem until now. In this thesis we consider this problem from the algorithmic viewpoint. In all of the algorithms we assume that the given hypergraph is 2-colorable and we want to color it. By using a simple construction, it was shown that for every r = 3, the problem of coloring of hypergraphs is as hard as the problem of coloring graphs. If NP ?= ZPP12, it is impossible to approximate the chromatic number of r-uniform hyhpergraphs with n vertices by a factor of n1-? for any fixed ? > 0, in time polynomial of n. In reference [KS03] a coloring algorithm with approximation factor... 

A coloring of regions is conflict-free if for any covered point in the plane, there exist a region that cover it, with a unique color. In this thesis, we examine the problem of conflict-free coloring of regions in dynamic model, with minimum colors, and with the possibility of recoloring the optimal numbers of colored regions. That means, regions are inserted one by one on the plane, and by inserting any region, inserted regions shall be conflict-free. Dynamic model are divided into three categories: offline model, online with absolute positions model and online with relative positions model. The difference between these three categories is in the information contained in insertion of... 

Structures that change color in an adjustable way have been noticed in recent years. There are structures in nature such as the skin of chameleons and octopuses and other animals that can change color. In recent years, inspired by these structures, materials based on photonic crystals or surface plasmonics have been proposed to change color. In this research, a review is made on these structures in nature as well as recent efforts to make such materials. In fact, photonic crystals create a special color due to the interference between scattered waves. For example, the change in the distance between the nanoparticles in the photonic crystals inside the chameleon skin is the cause of its color... 

In this study, the method of recognizing image patterns by image processing to guide the quadcopter to the landing point is expressed. For this, first the forces and torques on the quadcopter in the body system are calculated and after transferring to the inertial coordinates, the quadcopter dynamics with the use of Newton-Euler law is simulated in the MATLAB software environment. Then, a simple PID controller is designed to control the attitude, height and position of the quadcopter and create stability in the quadcopter dynamics. Because quadcopter navigation is dependent on visual data, a simulation environment called VRML is used. This environment has the ability to create a... 

We study Beck-like coloring of partially ordered sets (posets) with a least element 0. To any poset P with 0 we assign a graph (called a zero-divisor graph) whose vertices are labelled by the elements of P with two vertices x, y adjacent if 0 is the only element lying below x and y. We prove that for such graphs, the chromatic number and the clique number coincide.Also, we give a condition under which posets are not finitely colorable  

Scene classification is one of the most controversial fields in computer vision. It has many applications such as robot navigation and control, content-based image retrieval (CBIR), semantic organization of image databases, depth estimation and multimedia services. In fact the outcome of any classification system depends on the ability of the feature vector defined for the problem, by means of its distinguishing strength. In this research we focus on efficient feature extraction methods. In recent years, methods based on bags of features and special pyramid approach, have shown good performance in scene classification comparison to the others. So we based our proposed method on these ideas.... 

In the first part of this thesis we study Latin Square Graphs defined as follows: to each cell of a latin square L of order n we associate a vertex of the graph (which we call L3(n)) with two vertices u and v adjacent if and only if their respective cells are in the same row or column or contain the same symbol. We investigate the coloring problem associated with these graphs and explore the relationship between this problem and some other combinatorial objects such as strongly regular graphs and transversals and obtain some upper bounds. We use a computer search to find the chromatic number of all latin squares of order less than 8. We determine the chromatic number of some special classes... 

Nowadays, water pollution and water sources decreasion, is one of the important issues of our world. Treatment of polluted water and wastewater and recycling of those to industries and common uses, is very necessary. Dyes, is one of the biggest parts of water pollutants, especially, in textile plants. There are some ways for dye removal, in the industries; including biological, chemical and physical methods. Among of these methods, physical removal of dyes through adsorption (with Activated Carbon or other adsorbents), is very popular. Hydrogels are three-dimensional hydrophilic polymer networks, introducing very good swelling rate, mechanical properties and pollutants adsorption. In this... 

Graph sum coloring problem is a special case of graph vertex coloring. Because of its applications in practical areas, especially in scheduling, many researchers have been attracted to it. In recent years, several heuristic and metaheuristic algorithms were applied to sum coloring problem. In this research a heuristic algorithm based on mini-max ant system and simulated annealing metaheuristics is used for graph sum coloring problem. This algorithm is tested on random graphs used in the literature and compared with prior algorithms. Results show that in many cases our proposed algorithm reaches the best known results or improves them  

antum computers are necessary to simulate quantum systems. e fragility of qubits in presence of decoherence and external noise is the biggest obstacle in realizing a quantum computer. To overcome su problems, topological quantum computation has been introduced by Kitaev that combines the main quantum feature of the quantum world, namely, superposition of states, with the robustness of classical bits whi is the result of a macroscopic number of very small entities, comprising ea bit. In this way, topological features whi are robust against local perturbations are used for storing information. Kitaev’s model is a famous many-body model, whi has topologically degenerate ground states,... 

During the recent years, shortage of drinking water is one of the concerns of the society and necessity of purification of contaminated water are taken into consideration. Different methods to be developed to prevent problematic pollutions. Among these different methods the most common one is adsorption. In this thesis, the copper oxide nanoparticle was synthesized and its surface was modified using N-(2-aminoethyl)-3-(trimethoxysilyl)propylamine. The bi-amino surface functionalized nanoparticle was used to remove anionic dyes from single and binary systems. The scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDAX)... 

Graph coloring is an important concept in graph theory. There have been much developments in this concept recently, vertex coloring, edge coloring and total coloring are studied. But one of the newest kind of graph coloring is [r; s; t] -coloring. This coloring is introduced in 2003 by A. Kemnitz and M. Marangio. In this coloring the difference of any two adjecent vertices, any two adjecent edges, and any adjecent vertex and edge must be at least r, s and t respectively. In this thesis we study [r; s; t] -coloring of graphs and discuss about its results  

In this thesis, we study some bounds for the vertex chromatic num- ber and edge chromatic number of a graph. One of the most fa- mous theorems on graph colorings is Brooks’ Theorem, which asserts that every connected graph with maximum degree ∆(G) is ∆(G)- colorable unless G is an odd cycle or a complete graph. The following result has been proved: If every vertex of a graph G lies on at most k odd cycles for some nonnegative integer k, then χ(G) 1+√8k+9 . We recall from Vizing’s Theorem that the edge chromatic number of any graph must be equal either to ∆(G) or ∆(G) + 1. In this thesis, families of graphs that are Class 1 or Class 2 will be introduced.