Sharif Digital Repository

Graphene is a semiconductor with zero band gap. Due to electron ballistic transportation and having a single atom thickness of graphene, it is counted as an ideal material in Nano-electronic industry and essential candidate for fabrication of next generation of transistors. The Fermi level in graphene is located between Conduction and valance bands in a Dirac point. Due to low resistance, graphene has a substantial sensitivity near the Dirac point to local carrier density changes. This feature makes delicate detection of electromagnetic waves and gas sensing by graphene field effect transistors (GFETs). In this thesis, fabrication and characterization of graphene field effect transistor on... 

Microwave tubes are widely used in the telecommunications transmitters. high voltage power supplies are used to feed them. According to the specifications that arises for microwave tubes, To take advantage of these tubes need to maintain and stabilize voltage in a certain amount to be felt. If the tube supply voltage changes, the desired output parameters such as RF output power quality will change. To stabilize the voltage is within acceptable limits provided in different ways. One common method is the use of switching regulators due to the high efficiency compared to linear regulators considered. But it also will bring problems. Some of these problems can be pointed to electromagnetic... 

Cloud computing is a new computing environment where computing infrastructure, platform and software are provided as a service. Rapid growth of cloud environments has increased the importance of security requirements and challenges for both service providers and users in cloud. Two main security issues in software as a service (SaaS) delivery model are access control and privacy preserving in basic web services and also in composite services obtaining through the automatic composition and inference of policies from the ones specified for basic services. In this thesis, we present a privacy preserving access control model and framework for service composition in SaaS delivery model of cloud... 

The design and optimization of processes was focused in the past on economic issues such as profitability and return on investment, and less attention has been paid to environmental issues. In recent years, by introducing environmental criterion as pillars of sustainable development, environmental optimization of processes has becoming an inseparable element of the process engineering. Therefore, it is necessary to examine the compatibility of environmental indicators with economic objective. The purpose of this study is to investigate environmental indicators and economic objective function in optimizing the Crude Distillation Unit (CDU) of an oil refinery. The CDU is one of the most... 

One of the important issues that humans have faced in recent centuries is solving the problems caused by the entry of various pollutants into the environment. The entry of various pollutants such as dyes and pharmaceutical compounds is directly related to human survival. In this regard, one of the new methods of photodegradation of pollutants is through photocatalytic processes using semiconductors. Among semiconductors, TiO2 has attracted much attention from researchers due to its high photocatalytic properties, chemical and thermal stability, and availability. TiO2 has limitations such as low specific surface area, high band gap energy, and high electron-hole recombination, which has... 

In a solar central system plant about 40% of energy losses occurs in the heliostat field. Furtheremore, half of the investment costs for construction of the plant is related to the heliostat field. Therefore, an optimal design of the heliostat field is necessary for reduction of levelized cost of energy in solar tower power plants. In this study, in order to optimally design the heliostat field, first energy performance of the helistat field in one year is simulated. Solar power and sun’s position at each moment of the day is determined by mathematical relations. Then, loss factors in the field are modelled and heliostat field layout is designed by an algorithm. Finally, by using PSO... 

Today, due to the scarcity of fossil energy resources, security of energy supply, and increasing environmental concerns, we need to develop new technologies to promote energy-saving and reduce greenhouse gas emissions. One of the suitable options for this purpose is to use the simultaneous production of electric power, cooling, and heating. Meanwhile, trigeneration systems that provide part of their energy needs from the sun, due to the free solar energy source and low environmental impact, can be an ideal technology for clean and safe scattered production. The present study has suggested a trigeneration system of cooling, heating, and power generation based on the organic Rankin cycle and... 

Today, due to increasing electricity consumption and demand, the use of conventional systems such as thermal, hydro and nuclear power plants is not enough to convert energy. Over the past century, scientists have sought to discover new technologies for exploiting different forms of energy and converting them into high-efficiency electrical energy. One of these ways is to use the phenomenon of magnetohydrodynamics (magnetic fluid dynamics) to convert thermal energy directly into electrical energy. Magnetohydrodynamics is a theoretical field that studies the dynamics of fluids with electrical conductivity. Induction magneto-hydrodynamic generators use ionized hot plasma (a quasi-neutral gas of... 

The power generation system of this type of power plants operates on the air flowing through the power plant’s chimney and colliding with the turbine blades within the chimney. When the solar collector warms the nearby air and thus expands the air by absorbing the sunlight, a difference is created in the density. Then, this difference in the density creates the phenomenon of buoyancy, making the air pass to the top of the chimney through the collector.This study simulated and optimized a solar chimney power plant. The simulation and optimization were performed based on the information of Manzanares Solar Chimney Power Plant in Spain (located in 150 km from the south of Madrid). It was... 

The issue under discussion in this paper is to optimize the fuel consumption of the Toyota Prius hybrid car. In order to solve this problem, the ADVISOR design model used by NREL in the Matlab / Simulink environment has been used. Various parts of this model are described. The optimization performed on this issue is based on the emotional controller. This controller works by simulating learning in animals based on encouraging and punishing them. With the introduction of the controller, the model and its inclusion in the fuel consumption control and its implementation have achieved good results. In the initial state and the controller in the model, the fuel consumption was 4.9 liters per 100... 

In this thesis, an attempt has been made to provide a smart and innovative system to optimize fuel consumption in cars by using the combination of engineering sciences, aerospace, and machine learning. Considering the current challenges of societies, the economic importance of saving fuel, as well as recent developments in the fields of machine learning and reinforcement learning, this research tries to improve the performance of cars in order to minimize the air resistance force of car bodies. In this regard, deep neural networks have been used to learn the dynamics of aerodynamic forces and reinforcement learning algorithms, especially DDPG (Deep Deterministic Policy Gradient), have been... 

چکیده (انگلیسی) Prediction of traffic parameters is one of the most important needs in the field of intelligent transportation. Traffic forecasting allows people to choose the best times and routes to travel using various data such as date and time, events and weather conditions. Traffic forecasting helps reduce traffic in cities and save energy. This information is important for urban management; Because it provides the possibility of improving public transportation systems and traffic measures, and in this way, it is possible to propose the best solutions for managing traffic and increasing the quality of life of citizens. Although various parameters such as traffic speed, traffic...