Sharif Digital Repository

In this work, carbon nanotubes (CNTs) were synthesized via arc discharge in an aqueous solution. The role of iron catalyst in CNTs formation was investigated utilizing arc discharge in iron salts solution (Fe2(SO4)3 and FeCl3). Thermogarvimetric (TG) analysis showed the presence of multi-layered structures including multi-walled carbon nanotubes (MWCNTs) and multi-shelled graphite particles when processing was performed in DI-water. In the presence of iron ions, single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) were formed. The effect of iron ions (Fe3+) concentration on CNTs yield was investigated by Raman spectroscopy. The highest yield was obtained when... 

Constantly rising fuel prices and environmental consciousness have caused alternative transport solutions to be considered.Recently, batteries and electric vehicle industries have developed to become a reasonable alternative for gasoline powered cars. Plug-In hybrid electric vehicles could be connected to the electrical grid to be recharged. To ease the charging process, one solution could use an on-board charger to charge the electric vehicle. This charger should be able to be connected to a conventional outlet for convenience reasons and moreover, it should be a grid friendly charger in order not to pollute the electrical network. After studying the introduced structures for electric... 

Nowadays high efficiency and power density are desired for designing a power electronic converter. Technology advances in power semiconductor devices, makes it possible to design converters for operation in higher frequencies to reduce size of the converters. As the frequency is increased, switching losses and temperature is also increased, so designing a converter for high frequency operation needs some tradeoffs. LLC resonant converter as a promising solution for battery chargers has ability to adjust its output voltage during Constant Current and Constant Voltage modes. However, its operation mode would change based on switching frequency change. Therefore, for efficiency-oriented... 

Nowadays, due to gearbox drawbacks, the direct-drive wind turbines have received much more attention. Permanent magnet synchronous machines are commonly used for this purpose. The flux reversal machine with a magnetic gearbox and high power density could be an appropriate alternative. Due to placement of permanent magnets on the stator, the machine has a simple and robust structure and provides more reliability. There is limited study on optimization of the flux reversal machine and the existing papers are not complete and many parameters like PM dimension, working temperature, and winding reactance are not considered in the optimization process.Considering the flux reversal machine... 

As more renewables step in, the ongoing change will be drastic for the electrical grid. The energy sector must find new ways to balance energy production and consumption. Electric vehicle (EV) batteries are by far the most cost-efficient form of energy storage since they require no additional investments in hardware. A bidirectional EV charger is a new technology that enables energy to be pushed back to the power grid and auxiliary loads from the battery. The electrical requirements of the EV charger are examined in detail to find an appropriate power electronics converter to meet all the requirements. The CLLC resonant converter is a promising candidate for high efficient, bidirectional... 

Recent studies have indicated that one-dimensional titanium dioxide (TiO2) shows excellent properties in comparison to other forms of TiO2 materials in photocatalysis, sensing, self-cleaning coating and photovoltaic applications. In this project TiO2 nanorods were grown in polycarbonate template, with pore diameter of 200 nm, by solelectrophoretic deposition method. Firstly, properties of TiO2 sol were investigated. The average particle size of TiO2 (measured by zeta sizer instrument) was 17 nm and the zeta potential was around 45 mV, which confirmed good stability of the sol against aging. Moreover, FTIR analysis showed that a full conversion of precursor (titanium isopropoxide) was... 

Isolated electric energy systems are often needed to supply 3 kind of electric loads. This could be caused due to geographic isolation, the necessity of load mobility, demanded values of voltage and current that are not compatible with the local networks. This makes the design and construction of stand-alone energy systems a must. Because of sustainability concerns and enviromental pollution avoidance, Modern designs are being pushed towards cleaner energies and technologies. Polymer electrolyte membrane type fuel cells are among the new technologies that are being considered as a good alternative to the traditional power sources used for stand-alone energy systems. Although the basic... 

Video encryption algorithms have become an important field of research nowadays. As the increasing rate of employing videos in commerce and other visual applications , the security of video data is becoming more vital. A digital media can be transmitted easily in real time everywhere at any time due to the advanced development of communications, Internet and multimedia technology. As a result information availability has increased naturally with the introduction of mobile devices. However, this availability faces with the problem of maintaining the security of information that is transmitted in public channels.
The new version of video coding standard that is...