Sharif Digital Repository

People usually use trust and reputation when they encounter uncertainty in the nature. Graphs are good tools to model and analysis of trust’s problems. If we show human and computer agents by graph’s nodes and trust values by its edges, in literature, the output graph is so-called Web of Trust. Most recently, there are three major research areas in which trust is studied. First area is policy-based trust which uses policies, digital signature and authentication methods. Second area is reputation-based trust which uses reputation and social network tools to estimate trust where past interactions or performance for an entity are combined to assess its future behavior. Third area is trust... 

In this thesis, we study and analyze the performance of matched and partially-matched re-ceivers for a typical Ultra Wide-band Spectrally-Encoded Spread-Time (SE/ST) CDMA in the presence of multiple tone jammers and a coexisting OFDM system. We investigate a scenario in which there is not any information about the jammer and OFDM subcarrier frequencies in the transmitter side and we try to cancel jammers and interferences at the receiver. For this case, we demonstrate that by using a partially-matched filter at the receiver in an environment with multiple tone jammers and some coexisting systems the performance of the SE/ST system can be improved. We also assume K asynchronous users and... 

In recent years utilization of quantum dots for stem cells detection and clean energy production has received intensive attention. Graphene and its derivatives have been widely studied because of their effectiveness on electronical and optoelectronical devices, chemical sensors, nanocomposites, and energy storage. By use of metal nanoparticles, such as AuNPs, we can develop properties of graphene, and control them via shifting the absorption peak wavelength and increasing its biocompatibility. In this research, hybrid nanoparticles of gold-graphene as core-shell and conjugated by polymeric linkers containing amine or thiol functions are synthesized. Our purpose is stabilization the... 

Progress aerodynamic and structural applications has lead to solid-fluid interaction (SFI) engineering. One major application of SFI is to improve of aerodynamic characteristics of airplanes. One option is to use elastic shells.this field of study is so novel and a challenge for future researches. This what current thesis is focused on We use numerical simulation in both fluid and solid parts.In other word, we employ the finite –element method to solve the solid mechanics governing equation and the finite volume element method to treat the fluid dynamics governing equations. The fluid governing equations are 2D navier- stokes equations and the solid part is the 1D Euler – Bernoulli equations... 

With the rapid development of mico-nano propulsion systems in micro-spacecrafts and micro-sattelites, precise investigation of flow field in these devices has become necessary. Micro propulsion systems usually have a thrust in order of mili Newton, and they can be used for maneuvers of spacecrafts with mass of less than 10 kg. Micro propulsion systems are usually classified according to their thrust generation mechanism to different classes like cold gas, and chemical propulsion systems. Cold gas micro propulsion systems obtain their energy from thermodynamic expansion of gas and not by combustion. If the flow fiel dimensionare comparable to mean free path, rarefaction effects are observed... 

Novel manufacturing technologies in micro scales, such as micro machining, guide us through constructing micro scale systems known as MEMS. These systems have a wide range of applications, from fabrication of electrostatic, magnetic, pneumatic sensors and actuators to micro mechanical gears and motors. Also, MEMS applications involve the manipulation of one or more fluids, known as microfluids. Simulation of flow through microchannels over nano particles has important applications in solid particles transport. In this flow, the rarefaction phenomenon will affect the flow behavior and its subsequent impacts such as aerodynamic drag forces. In this work, we use the Lattice Boltzmann method... 

It is well known that the most rigorous method to assess the performance and to predict the seismic demands of a structure subjected to earthquake is nonlinear time history analysis. However, this technique is accompanied by complexities and difficulties in evaluating the seismic demands of structures and requires superior knowledge and skill. As a result, in recent years, nonlinear static analysis has been proposed in performance based design procedures. One of the primary assumptions of nonlinear static procedures is that the behavior of a structure with multiple degrees of freedom (MDOF) subjected to seismic ground motion can be estimated from the response of an oscillator with a single... 

Hydrogen fuel cell is one important choice to supply energy for vehicles in near future. The lack of a safe but inexpensive technology to store hydrogen in a vehicle tank is a serious challenge to commercialize the application of fuel cells. Past experiments have shown that carbon nanostructures, especially single walled carbon nanotubes, have considerable capacity to boost up hydrogen storage. Therefore, many studies have been performed to investigate the possibility of higher hydrogen storage capability using nanostructures for the past decade. Molecular dynamics method which is considered as one of the most important tools in studying nanostructures has shown vast applications in these... 

A global rotating atmosphere with polar vortex and super rotation is simulated using a simplified Venus General Circulation Model (GCM). The polar vortex is maintained strongly by meridional circulation develops in the form of a simple Hadley cell, extending from the equator to the pole in both hemispheres and rotation terrestrial planet. Venus Total Polar Vortex Parameter (PVP) was defined like globally integrated super-rotation but at polar skullcaps (60-90 deg). Venus Polar Vortex Parameter is PVP=1.5 that’s qualitatively similar to observed polar vortex. Then with study in terrestrial planet and Titan modeling, we appointed the Polar Vortex Parameter and critical limit of Polar Vortex... 

Dynamic behavior of space structures are of great complexities. On the event of severe earthquake these structures exhibit high resistance and on the other hand, their high rigidity and small deformation makes it necessary to pay attention to their dynamic behavior, especially when combined with other types of structural systems. Also due to lack of sufficient codes and references, their dynamic behavior is still unknown to a great extend. Among these kinds of structures, reinforced concrete double curvature shells, and especially funicular shells, are much more important than others. In this thesis, dynamic response of these kind of structures, especially reinforced concrete domes, in... 

With a fast progress in nanotechnology devices and components, e.g., MEMS/NEMS, heat transfer study in micro/nanoscales has become so critical for the systematic design and precise control of such miniaturized devices towards the integration and automation of Lab-on-a-chip devices. Demands in high heat transfer rates have returned the concerns to impinging jet cooling systems. However, studying impinging jets in the micro/nano scales is requires the molecular dynamics knowledge to analyze the true micro/nanoscale flow behavior accurately. According to the importance of this subject, we use direct simulation Monte Carlo (DSMC) method to simulate nano impinging jet gas flows. The thesis is... 

Findings of economics in last decade shows that social and economic institutions have direct influence on economic performance of a society. However, these institutions are determined by the state. In different regimes, the political power is in the hand of different social groups with different preferences and goals; as a result, different social and economic policies and institutions are take place in different political regimes. In this research, we study economic performance of a society under control of two different political regimes: in first, the majority rules the state and in second, there is a totalitarian regime in which; the political power is concentrated in hand of a group of... 

The role of government in economy has been a controversial subject in economics. Lately, there has been some fundamental change in evaluating this subject. One could mention two of these as 1) realizing the importance of micro-founded macro model for evaluating policy, and 2) taking into consideration the rent-seeking behavior of politicians. In this research, a general equilibrium in a micro-founded macro model will be discussed and then in political economics framework, the effect of government on this equilibrium will be investigated. Only the redistribution role of government has been considered. First, the model in which a benevolent government is seeking optimal policy is Discussed.... 

To investigate boiling heat transfer characteristics of nanofluids, transient quenching¬ experiments of a high temperature silver sphere in water-based nanofluids with Ag and TiO2 nanoparticles were performed. A silver sphere of 10 mm in diameter at the initial temperature of 700o C was quenched in the nanofluids at the temperature of 90o C. The results showed considerable reduction in the quenching ability of nanofluids compared to that of pure water. The presence of nanoparticles in water caused film boiling mode to vanish at lower temperatures depending on the mixture concentration. Computed heat transfer rates in nanofluids were lower than those in pure water. In the quenching... 

With altering natural state and increasing impervious surfaces, traditional urbanization leads to deteriorating the environment and water catchments. During the years most efforts in order to control the urban runoff outflow, have been focused on quantity; and awareness about improving water quality has been raised just in the last few years and, which emphasizes on pollution source control. Standard water quality sampling methods are time consuming, expensive and because of sampling in broad geographic areas, difficult; however modeling is a more efficient way in assessing water quality and as worries about non-point source pollution grows, different kinds of models have been used to... 

The notable share of housing sector in GDP (approximately five percent) shows this sector’s relation with macroeconomic activities. On the other hand, House as an asset leads housing sector to be affected by monetary and fiscal variables. A dynamic panel data was used in this study to evaluate the relations between housing sector and some macroeconomic variables in metropolises of Iran. As results show, in long term growth of liquidity, GDP per capita and sharp ratio have positive effects, and land per capita has negative effect on housing price in metropolises of Iran. Price increases have not been equal in different cities. Inequality of land price between metropolises and between...