Sharif Digital Repository

The running time of almost every algorithm in the graph theory depend on the number of edges. Thus, these algorithms are often too slow when the input graphs are dense. Therefore, it is useful to reduce the number of edges by sparsification. In fact, sparsification is the task of approximating a graph G = (V;E) by another graph ~G = (V; ~E) so that ~E E (j~Ej jEj) and ~G maintain a main prefixed property of G. Depending on these properties several notions of graph sparsification have been proposed. In this thesis we study a notion of sparsification that is called spectral sparsification which is based on the contributions of Daniel A. Spielman et.al..In this notion of sparsification... 

By using an encoding scheme based on Algebraic Integers (AIs), we study in this thesis how to map the real numbers needed in the computation of the FFT to integer numbers, in order to prevent error production and propagation throughout the intermediate stages of the FFT computation. To reconstruct encoded data, a decoding stage is to be used at the end of the FFT computation. AI-encoding poses two challenges; how to determine suitable AI bases and an unwanted growth in the number of data passes. This research work, firstly, determines an appropriate FFT architecture, and then, proposes a dedicated architecture based on AI-encoding. The basic and also the proposed dedicated architecture are... 

Nowadays, power systems and substations are the most important components of the vital infrastructure of a country, which handle the production, transmission and distribution of the electrical energy. Automation systems increase the efficiency of the power industry while making remote control possible, but the use of computer-based control systems is a potential field for cyberattacks which may cause equipment destruction and electricity network destabilization. One of the main requirements for the utilization of digital substations is the synchronization between different equipment used in it. Several algorithms and protocols have been proposed so far for time synchronization in distributed... 

With the advent of new technologies in everyday human life, issues related to the use of vehicles have become crucial subjects of investigation. In this context, vibrations transmitted from the vehicle to the human body, especially in terms of long-term health effects, have garnered special attention and significance. The main objective of this research is to develop a control system for the active control of vibrations transmitted to the human body. To achieve this goal, a 5-DOF model of the human body has been employed as the study system. Considering the uncertainties in the parameters and dynamics of this model, H∞ and µ-synthesis methods have been utilized for robust control design. The... 

Nowadays, horizontal drill string is a powerful tool for drilling in the oil and gas industry and an efficient method for constructing underground tunnels in cities. Despite its many uses, this method is exclusive to limited countries and is considered among the most advanced methods for drilling. One of the most important problems in the field of horizontal drilling is the existence of destructive axial, torsional and lateral vibrations. If these vibrations are not controlled, they can cause irreparable damage to the plant and drilling well. Among the introduced vibrations, axial and torsional vibrations have a very dominant effect on the drilling process, so the purpose of this research is... 

Through the last decades, due to environmental issues and to confine CO2 emission and also dependency to the fossil fuels, renewable energy resources has been developed. It’s been expected up to 2035, the renewable energy resources will be scaled three times and among those resources, the wind energy will stand prominently. Out of this king of renewable resource, the horizontal wind turbine has been subjected in this research. The focus of is to design the controller in third of a 2 MW turbine operation by which stable rotor speed and nominal output power to be attained. Besides, to enhance the accuracy of the wind turbine profiles, the TURBSIM software (At the National Renewable Energy... 

Through the last decades, due to environmental issues and to confine CO2 emission and also dependency to the fossil fuels, renewable energy resources has been developed. It’s been expected up to 2035, the renewable energy resources will be scaled three times and among those resources, the wind energy will stand prominently. Out of this king of renewable resource, the horizontal wind turbine has been subjected in this research.The focus of is to design the controller in third of a 2 MW turbine operation by which stable rotor speed and nominal output power to be attained. Besides, to enhance the accuracy of the windturbine profiles, the TURBSIM software (At the National Renewable Energy... 

Design, simulation, optimization and manufacturing of an enzyme-based microfluidic biosensor has been carried out during this research to measure histamine concentration in a sample. The designed biosensor is composed of a micro-bioreactor to degrade histamine and yield hydrogen peroxide, and a chemical reactor to measure the amount of hydrogen peroxide, using chemiluminescence methods. The geometry of the bioreactor and chemical reactor is developed through comparison and optimization of several different geometries. In theory, the designed sensor can determine histamine concentration in a range of 10M to 1mM under one minute, with a maximum error of 5%. Designed biosensor is built using... 

Among cryptography devices, resource constrained devices like sensors, RFID tags, smart cards and etc need a special class of cryptography algorithms. These devices have three limitations: memory, consumed power and computing power. Therefore, need a special class of cryptography algorithms that is lightweight cryptography. Lightweight cryptography systems have features and limitations that make them more vulnerable against attacks such as power analysis attacks. For this reason strengthening them against these attacks need more attention. So far, various countermeasure for secure implementation of different cryptography systems proposed. Most of them trying to decrease the correlation... 

In this study thermodynamics and kinetics effects of two ionic liquids (ILs) on the formation and dissociation of methane and carbon dioxide hydrates were investigated. The ILs used in this study are 1-butyle-3-metylimidazolium tetrafluoroborate, [Bmim][BF4], and 1-butyle-3-metylimidazolium methyl sulfate, [Bmim][MS]. At the first step of experimental section, the tetrahydrofuran (THF) was used in atmospheric pressure. The structure of THF hydrate is similar to natural gas hydrate; therefore it is used as a model for studying the properties and investigation of inhibitors effects on gas hydrates. In order to consider the effects of foregoing ILs on the formation and dissociation of gas... 

The IEC61850 Standard was introduced for IED, Intelligent Electronic Device, in a power substation so that different devices from different manufacturers could work together. Each of these devices must be configured to start communication. Chapter 6 of the IEC61850 Standard discusses the configuration language of these devices, SCL, Substation Configuration Language, as well as how to write it in detail.A failure or denial-of-service attack can occur in a power substation if a tampering or embedding a breach in devices’ configuration occurs. To discover such attack, one can model the behavior of all the components in the SCL language using a language describing the behavior, and then compare... 

In this thesis, combustion of liquid fuel spray under the condition of hot and diluted oxidizer, has been investigated. To this end, a novel type laboratory-scale test rig was designed to study the physics governing the MILD-Spray combustion conditions with an applied approach. The underlined test rig eliminates the operational problems of its predecessor test stands and is used for a heavier fuel with much more complex chemical composition (kerosene). The test section is axially symmetrical, in which the fuel is injected by a pressure-swirl atomizer in the direction of hot and diluted co-flowing air. With the use of the aforesaid test rig, the effect of variables such as oxygen...