Sharif Digital Repository

A novel broadband and tunable terahertz (THz) source based on the modulation instability phenomenon (MI) is proposed. By introducing higher-order dispersion terms in nonlinear Schrodinger equation (NLSE) the MI gain is spread toward larger frequencies which in turn shifts the input optical frequency to the THz range. In this method, the need for any further pump signal is eliminated while the input power is reasonable, less than 1W, due to using EDFA fiber. By changing the input signal power, the generated THz signal frequency could be tuned. The proposed structure is numerically simulated in the designed values of dispersion orders  

This research deals with one of the current issues in the world and in Iran, which is named the field of cryptocurrencies. Domain that is managed decentrally due to the use of blockchain platform. This decentralization has caused different challenges (security problems, disruption of economic governance, etc.) for governments and has created different advantages and disadvantages for each country. This study seeks to investigate how Iran is facing the challenges in the field of cryptocurrencies. In this research, three main questions have been asked to determine the situation of Iran in the field of cryptocurrencies. In the first question, what are the policies of Iran is questioned and then... 

This research deals with one of the current issues in the world and in Iran which is called the field of cryptocurrencies. This research has tried to map the situation of cryptocurrencies in the world and then the situation of Iran in this field.In order to understand the situation of Iran in the field of cryptocurrencies, three main questions have been defined. The Questions that first express the nature of Iran's policies and then determine the position of these policies in relation to the conceptual framework, and then it will discover the reason of the adoption of these policies in Iran.Therefore, this research has an exploratory approach and its research method is qualitative. In order... 

Peer-to-Peer networks are invented to enable participants (peers) to share their resources and find and use the shared resources of the others. So the main issue is the mechanism of finding granted resources of the other peers. In Peer-to-Peer networks, there is no central server to index shared resources of the peers. So peers should collaborate to provide a fully distributed mechanism for searching resources. Considering the huge size of peer-to-peer systems, it is apparent that efficiency of the search mechanism is very critical. In this thesis, to have efficient seach in Peer-to-Peer networks, we propose two approaches. Then based on these approaches, we propose the third approach to... 

In this thesis the effects of impurities and different defects on electrical and magnetic properties of monolayer and bilayer graphene is investigated. Calculations are performed using density function theory. Alloying monolayer graphene with boron and nitrogen the energy gaps of 0.7 and 0.6 eV are obtained, respectively. Moreover, we show that BN is a good candidate for opening the band gap in graphene. Alloying monolayer graphene with BN the energy gap of 1.2 eV is obtained. Another way of opening band gap is to somehow break the symmetry between layers of the bilayer graphene. By alloying one layers of bilayer graphene with B, N or B-N, although the symmetry of layers is broken, each... 

As steel shear walls are usually applied in the central cores of buildings (around the elevators and stairs), the use of opening as door is inevitable in steel shear wall spans. On the other hand, because of weakening the performance of steel shear walls due to the presence of these openings, it is necessary to apply stiffeners around it. The use of stiffeners around all sides of opening continued to beams and columns, is very expensive. Therefore, the necessity of studying on the effect of different arrangements of stiffeners on the behavior of steel shear walls is felt. In this research, a number of steel shear walls with different characteristics in terms of plate aspect ratio, location... 

Population growth require increasing demand of Energy. The fossil fuels are the main source of energy. However, they are main source of carbon dioxide emissions. Considerable amount of fossil fuels is used in the power plants. Increasing trend of electricity consumption as well as the lack of alternative fuels such as renewables in the short time will increase the consumption of fossil fuels and emissions. The most important greenhouse gas emitted from the power plants is carbon dioxide. That's why the separation of carbon dioxide from the gas stream of power plants is necessary.Separation of the carbon dioxide by adsorption is considered in this project both experimentally and... 

Due to the ability in producing nanostructured materials, Mechanical Alloying has gained outstanding position in comparison with other materials fabrication techniques. In this research,with different milling condition, Alloying of Ni-Ti-Ag was performed. In order tofabricating the alloy, twodifferent initial materials were employed.In one process, nickel, titanium and silver were used as raw materials, and in another, titanium hydride was used instead of titanium.Initial powders were investigated in planetary mill, SPEX mill and vibratory disc indifferent times. Using XRD, microstructure information and phase analysis was obtained. EDS was employed for determination of elemental...