Sharif Digital Repository

Nowadays, according to increasing development of construction industry in the world especially in the building area, the need to use technology and innovation for fabrication and maintenance of this industry has increased. And this fact becomes apparent that the use of traditional systems of construction isn’t tailored the countries’ requirements anymore. One of the construction industry’s limitations is the restrictions on architectural designs reys. The columns are among the most important components of structure and have a major role in bearing all gravity and lateral loads and transferring them to the foundation. The failure or destruction of the components in the structure under applied... 

The aim of this thesis is to introduce some algebraic topologies methods and apply them on fining the chromatic number of some famous graphs and also hypergraphs. In the first part, we will use a mixture of two well-known technics, Tucker lemma and Discrete Morse theory to find an upper bound for the chromatic number of s-stable Kneser for some specific vector s. to find the sharper upper bound, we will deviate our strategy and use another approach by finding an edge-labeling and apply some theorems in POSET algebraic topology. In this way, we also find a connection between Young diagrams and the numbers of spheres in the box complex related to Kneser graphs and hypergraph. Actually, we can... 

Fossil fuels provide the most needs of the world's energy, however, continues to lead to two key problems. The first problem is their limitation, and the second problem is the creation of serious environmental issues. Therefore, the need for renewable energy sources is felt more than ever.As an energy source, hydrogen is the lightest, most efficient and cleanest fuel. One of its unique properties is efficiency, the production of electricity by fuel cells through the electrochemical process, has far greater efficiency than of mechanical energy production from fossil fuels in internal combustion engines or energy production in thermal power plants. A fuel cell is a device that converts... 

Optimizing optical tweezers and achieving powerful traps has always been a challenging topic for researchers , since the trap stiffness increases with increasing laser power which may damage specimens , especially biological ones and cells . In this thesis , we introduce a special geometry and structure of particles that , have the possibility to increase the stiffness (strength) of the optical trap and cause the magnetic response of particles at optical frequencies . Special geometries such as a combination of dielectric particles with magnetic nanoparticles that emphasize the role of the laser magnetic field and lead to changes in the electrical and magnetic properties at the laser... 

Today, energy crises and the environmental pollution have become serious problems for the human being. To address these problems, extensive efforts have been made to replace fossil fuels with other clean energy resources such as fuel cells. In the meantime, polymer electrolyte fuel cells are very important as they are now commonly used in the field of transportation, and their importance become even more obvious as we consider the fact that the by-products from electricity production by such cells are simply water and heat. This research studies the efficiency of the polymer called “polysulfone” as an electrolyte fuel cell, which has the above named mechanical thermal and chemical... 

Optical tweezer is a highly focused laser beam that could be used to trap micro and nano particles in three dimensions. It could be used to measure(or apply) piconewton range forces. Most of the optical tweezers experiments have been done in liquid mediums. In last few years, trapping particles which are floating in gas mediums(called aerosols) have been considered extensively. In this thesis, the changes in trap stiffness and conversion factor due to changes in laser power, trapping depth and particle are evaluated. It is shown that changing these three parameters, cause considerable changes in trap stiffnes and conversion factor. Linear behavior of trap stiffness versus laser power,... 

In this study, the seismic response analysis of a buried pipeline had been performed using three-dimensional (3D) dynamic analysis of the soil-pipeline interaction under different loading inputs. A number of parameters such as properties of the buried pipeline including diameter and internal pressure and different loading frequencies were used for this investigation. The pipe was considered as an elastoplastic material and a nonlinear elastic material based on the Mohr–Coulomb criterion was used to model the soil behavior. In addition, pipe-soil interaction has been studied in both tangential and vertical directions. The ABAQUS software was utilized for the 3D numerical modeling and... 

One of the main requirements in today’s computer networks such as the Internet is protecting the privacy of users. Hence, anonymity is a useful tool for privacy and provides user’s anonymity. So far, several protocols have been designed to provide anonymity but most of the times, attackers found a way to take advantage of weaknesses in the design and implementation of these protocols. There is a class of attacks,where attacker tries to relate clients of anonymity system to each other, regardless of the communication protocols they use, just by observing networks traffic.The MIX technique forms the basis of many popular ervices that offer anonymity of communication in open and shared networks...