Sharif Digital Repository

Nowadays, by development of technology and population, rivers have been faced environmental issues. In one hand, due to the several factors that can affect rivers pollution, it is not easy to propose a comprehensive solution for the above mentioned issues, while, on the other hand, it is necessary to address and resolve some of these issues as soon as possible. Considering rives as a system, there are lots of economic, political and quite a few other factors which try to change the condition to their own interest. In order to find a solution that satisfies all the effective parameters up to a certain limit, a mathematical tool, called the Game theory method, is utilized. In this research, we... 

Today, the process of corrosion and compensation of minor injuries, without the need for tracing or any other physical interference, has become one of the subjects of interest to researchers. Inhibitors have been considered as one of the anti-corrosion agents. In this research, safflower extract as a green inhibitor in sodium chloride corrosive environment was used to evaluate the rate of corrosion of mild steel. Also the MoS2 nanoparticles were used as carrier of this green inhibitore in the epoxy coating to allow the activation of the coating in a scratched state in sodium chloride solution of 3.5%. In the first step, the extract of the safflower was prepared to reach the best part of this... 

Hydrothermal supercritical method is one of the most suitable methods for metal oxide nano powder, ceramics and mineral catalyst synthesis. Metal oxides nanopowder in its pure or mixed form has wide potential application as chemical industrial catalyst, hot Superconductors, magnetic material, gas sensors and car catalyst convertors. One of the most important metal oxides aspects of application is uranium oxide as nuclear reactor fuel is used. In addition, UO2 is selective catalyst for converting methane to methanol process and Decomposition of organic Chlorine material. In Supercritical hydrothermal method done in high pressure reactor with critical to fluid, is new method for the... 

Superalloys are widely used in aerospace and power industries due to the good performance at high temperatures for examples gas turbines, steam turbines and aircraft components. In addition to the turbines cobalt-base superalloys are used in medical implants such as knee and hip joints. The main strengths of the superalloys are heat-resistant, retaining their high mechanical and chemical properties at high temperatures, high melting temperatures, high corrosion resistance, resistance to thermal fatigue, thermal shock, creep, and erosion. Because of difficult to machine properties of superalloys, grinding is one of the effective methods for machining superalloys. The surface integrity of the... 

Drilling super alloys with a good hole quality and acceptable surface finish is a constant challenge in modern industries dealing with such materials. Ultrasonic assisted drilling is a modern and nonconventional method of drilling which has attracted many researchers attention recently. In this study deep drilling on Inconel 738 LC is done using ultrasonic assisted drilling technique and the results are compared with those of Electro Discharge Machininng or EDM method. The results show that Ultrasonic Assisted Drilling or UAD is an appropriate alternative for EDM of Inconel. The whole process time is decrease dimensional accuracy is improved and surface roughness is decreased significantly.... 

Due to popularity of mobile wireless devices, security of mobile ad hoc networks (MANETs) being more important than before. Traditional key management schemes based on symmetric key cryptography are became ineffective because of dynamic and infrastructureless nature of these networks.Recent studies are mainly based on traditional public key cryptography schemes and ID-based cryptography schemes. On the other hand, Contributory schemes seem suitable for MANETs because of their inherent self-organize property. Key update and Key revocation are the fundamental issues of key management schemes in mobile ad hoc networks. Certificateless public key cryptography, in addition to solve those issues,... 

International trade arrangements have been considerably developed in recent decadees. Especially, one can note the role of these factors in economic development and improvement of life standards in member countries. In the meantime, Economic Cooperation Organization (ECO) was established in 1985, by Iran, Pakistan and Turkey and then extended by seven other countries: Afghanistan, Azerbaijan, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan. Improving economic development and intra-group trade of member countries is one of the main objectives for the group. The purpose of this research is to estimate the ex-post effects of ECO on the intra-group trade of member countries.... 

Establishing an efficient free trade agreement (FTA) requires some conditions in both trading partners. The median voter approach insists on the direction of general interests (identified by the utility of a median voter) to explain how two countries may agree to sign an FTA. At the other side, lobbying approach emphasizes on the role of interest groups (groups with a large influence on the public decisions) in forming FTAs. Taking into account the theoretically based and empirically robust foundation of the median voter approach, we rely on it to investigate the major determinants of free trade agreements in the case of ECO countries besides all their main trade partners. The database... 

During the two last decades, Iranians have faced with a wide and substantial increase in housing prices, especially in great metropolitans such as Tehran, Mashhad, Isfahan and Shiraz. This easily could be refered to a hyperinflation which significantly impeded the access of low and medium income families to housing. This study uses a structure model to recognize the responsible factors of such a rise in housing prices and to show whether there is any price bubble in market. The model consists of both supply and demand side determinants to explain the price changes across Iranian provinces over 1375-1390, in a panel data context. In particular, we use a longer and larger database which also... 

Delamination is a major problem in drilling of fiber-reinforced composite materials. Thrust force is an important factor leading to propagation of delamination during drilling process. One of effective methods to reduce machining forces is application of ultrasonic vibrations. In this study ultrasonic assisted drilling is applied to reduce thrust force in drilling of GFRP laminates. In order to conduct experiments a setup is designed and fabricated to apply both vibrations and rotation to drill bits. Using Taguchi method, a set of experiments is conducted with feed rate, spindle speed, point angle and ultrasonic vibration amplitude as control factors. The results show that applying... 

U-shaped assembly lines usually are more effective than straight lines. Therefore special attention has been paid to u-shaped line balancing problem in recent years. On the other hand most articles on the line balancing problems are investigated for the first time. However, within the lifetime of an ALB, the balancing problems do not occur only once prior to its construction, but rather continuously as rebalancing. For example whenever the demand structure or production technology changes or producing seasonal products, the ALB needs to be reconfigured. So many balancing issues in the real world are related to re-balancing of production lines.
Therefore in this study, U-shaped assembly... 

In this thesis, we statistically model and analyze one of the main systems in optical communications which are based on Second HarmonicGeneration (SHG) process. To this end, we first introduce various applications of this process in optical communication systems and see that the main application of this nonlinear process is in the process of optical clock recovery in both of OTDM and SPE_OCDMA networks. In the rest of the thesis, we characterize the mathematical structure of these systems and use that to statistically analyze their behavior. In considering the optical clock recovery system based on SHG, we introduce three intrinsic sources of timing jitter in the system, namely, the On-Off... 

Foreign direct investment (FDI) has considerably increased in recent years and achieved two percent of the world GDP in 2009. The positive impact of FDI on many national economic variables such as export and employment has been a great motivation for countries to seek it. In spite of many promoting factors in Iran, the Iranian FDI inflow still remains small. Using a huge panel dataset including 2604 real observations, this study aims to recognize and evaluate the impact of main factors influencing FDI inwards across the world. Based on a theoretical approach, we develop an empirical gravity model which includes not only the traditional mass variables but also some specific factors to FDI...