Sharif Digital Repository

Satellite attitude determination means specifying its rotation relative to a known reference. To determine satellite attitude, gyroscope is used to measure angular velocity and attitude sensors such as sun sensor, magnetometer, star tracker and earth horizon scanner are used in order to obtain vector measurements. In kinematic control, satellite angular velocity is determined in a way that its attitude converges to desired attitude. Usually, gyroscope and attitude sensors measurements are contaminated by noise which leads to errors in satellite attitude estimation and control. In the literature, gyroscope and at least two vector meaurements are used to estimate and control the... 

In this era of competitive markets, firms and organizations can survive that have a competitive advantage through their business models. Having a competitive business model and its frequently evaluation is one of the secrets of success. Another, especially of these days, is digitalization of many businesses. Every day in our business environment new digital businesses are establishing. Conversely emergence of the Internet affected many of current businesses, then this question be arose that, what and how this phenomena can affect the current business models? Abstract (Max. 300 words for M.S and 500 words for Ph.D. theses) In this research we will check this affect on the automobile after... 

Nano and microsize H-ZSM-5 were synthesized by hydrothermal crystallization method with same batch composition to investigate the effect of crystallite size of H-ZSM-5 in the methanol conversion to propylene (MTP) process. The average particle size of nano and microsize H-ZSM-5 were obtained in the range of 0.15- 0.2 and 1- 2 µm, respectively. Also, optimized catalyst of Petrochemical Research and Technology Company was synthesized using terapropylammonium bromide as template. Nowadays, terapropylammonium bromide (TPABr) is cheeper than terapropylammonium hydroxide (TPAOH); therefore we used it as tamplate. Activity tests were conducted at operating conditions of T= 460˚C, P=1 atm and WHSV... 

Wettability of reservoir rock is one of the effective parameters in determining the mechanisms of production and consequently the amount of residual oil inside the porous media. In addition, the salinity of injected water is important factor in the recovery of reservoir oil in waterflooding.On the other hand, the role of the hysteresis on the residual oil saturation as well as the flow functions such as relative permeability curves is very important. In this project, the effects of reservoir wettability and injected water salinity on the hysteresis and residual oil saturation in two-phase water-oil flow systems are studied. Core-scale experiments were carried out using sandpacks and were... 

The continuous rise in electricity demand and the ever growing power generation in different power networks over the world have caused the short circuit level in the power systems to exceed the operational rating of the installed power devices (including cables, circuit breakers and buses). Replacing these devices with new higher rating devices is an expensive solution. From this point of view, utilizing fault current limiters is an economical solution. Superconducting fault current limiters form an efficient category of current limiters. This type is expected to be studied and used widely in future due to their advantages. In this thesis, the first chapter reviews the superconductivity... 

Terahertz waves which includes frequencies between 100 GHz to 10 THz of electromagnetic spectrum have found many applications in science, medical treatments and industry. One of the recent methods to produce these waves is using nonlinear properties of superconductors based on Josephson junctions which inherently appear in some superconductors called BSCCO. Stack of intrinsic junctions of these superconducting materials can radiate terahertz waves by only applying a DC voltage across them. This Thesis investigates some of these structures based on Josephson junctions to produce coherent radiation of terahertz waves. For the optimization of the radiation power, this study also investigates... 

There are different approaches in modifications of General Relativity as the theory of gravity. The modified theories of gravity are important cases in this context, which mostly start by modifying the Einstein-Hilbert action, while keeping the general covariance. Within the modified theories of gravity, we consider two cases. The first is the f(R) theories of gravity, and the second is curvature squared theories of gravity with an action like S = ∫d4x pg( 116GR + (R)2 + R2 +(R)2). Curvature squared theories of gravity have interesting feautures, most important of which is renormalizability, in contrast with General Relativity. But this advantage, as noted by K.S. Stelle in 1977 comes at... 

Multiverse scenario has been recently addressed by physicists and they have found it useful in many areas of physics. In this dissertation, I have treated some issues about multiverse such as the kinds of multiverses, the arguments for or against multiverse, areas in which multiverse is introduced, etc. This dissertation has six chapters and an appendix. In the chapter one, some classifications of multiverse is introduced, and also some definitions of the concept of a world is presented. Then, my classification and definition of a multiverse and a world is introduced. In the chapter two, the concept of possible worlds in philosophy and its relationship with multiverse hypothesis is examined.... 

Near Horizon Extremal Geometries (NHEG), are geometries which may appear in the near horizon region of the extremal black holes. These geometries have SL(2;R)U(1)n isometry, and constitute a family of solutions to the theory under consideration. In the first part of this report,their thermodynamic properties are reviewed, and their three universal laws are derived. In addition, at the end of the first part, the role of these laws in black hole thermodynamics is presented. In the second part of this thesis, we review building their classical phase space in the Einstein-Hilbert theory. The elements in the NHEG phase space manifold are built by appropriately chosen coordinate transformations of... 

Employing high-temperature superconducting (HTS) tapes, instead of copper or aluminum wires for winding in a superconducting transformer, results in a series of significant advantages; such as: smaller volume, lighter weight, higher efficieny, greatly extended overload capability, better voltage regulation, lower life cycle cost, fault current limiting capability, lower environmental pollution and lower risk potential against fire hazards.In this thesis, optimal design of flux diverter using genetic algorithm for axial short circuit force reduction in HTS transformers has been performed. Then, multilayered flux diverters have been proposed for reduction of weight and losses. The impact of... 

Valve leak detection is very important due to bad direct effects on parts life and engine power. Acoustic emission (AE) has a good known ability on leak detection between fault detection methods. The aim of this thesis is presenting the ability of AE method for valve leak detection in internal combustion engines. The research method in a general framework based on the idea that firstly some evaluations were done in static tests for leakage due to three faults including clearance, quasi-crack and notch. Then, the evaluations were continued with dynamic analysis of rotational speeds and different loads on the engine. Finally, the neural network approach was used to automatically detect all... 

In this study biological denitrification method by moving bed biofilm reactor is investigated. The main advantage of MBBR reactor is due to their capacity for high removal rates and low operational problems such as clogging. Two MBBRs in series with 3 liter volume each, were designed in experimental set up and used in this research. Nitrification reactor worked under aerobic conditions and denitrification reactor operated under anaerobic conditions. Methanol was used as carbon source in the reactors throughout the study. Fifty percent of each reactor volume was occupied with KMT1 packing. To finding the optimum nitrate loading rate, the concentration of ammonium and nitrate were changed from... 

In power system operation, the term "operation planning" carries a wide range of meaning. For some utilities, operation planning denotes primarily short-term planning tasks (up to several days), such as load forecasting, unit commitment, hydro-thermal coordination, transaction pricing, fuel allocation, and security analysis while for other companies operational planning is interpreted in a wider context, and include mid-term planning activities (up to several months), such as maintenance planning, fuel budgeting, rate forecasting, network planning, relay coordination, etc. The mid-term planning provides the link between the long-term and short-term planning programs. The duration of this... 

Due to advantages of Peer-to-Peer (P2P) networks, many internet users use them for content distribution (Many internet users distribute content using them). These systems may be categorized to Centralized, Pure, and Hybrid. Gnutella is a heavily decentralized and unstructured file sharing P2P networks that are responsible for a good part of the traffic on the internet. These P2P networks are at risk of many security threats from internet worms. Internet worms and their threats are a major concern to the networking community. In this thesis we concentrate on passive non-scanning worms and propose a novel approach to detect such worms. As part of our work, we collected data from the Gnutella...