Sharif Digital Repository

Nowadays, metal-polymer dissimilar joints have attracted the attention of many industries, and the aplication of these joints in various industries such as automotive and aerospace is increasing. However, due to considerable differences in physical properties of metals and polymers, proper bonding between these materials is not easily possible, and metal-polymer joining remains one of the major challenges in the development of advanced composite structures. The adhesive/friction stir joining hybrid process is a relatively new idea that has been proposed to achieve longer lasting bonds and more safe structures. Using this process for metal-polymer joining can take advantage of both methods;... 

Website Fingerprinting is a trac analysis attack that allows an eavesdropper to determine the web activity of a client, even if the client is using privacy technologies such as Tor. Recent researches have shown that an attacker is able to detect which websites a user is visiting over than 98% accuracy, While previous countermeasures fail against this kind of attacks. In this research, we introduce two defenses. In the rst defense, we exploit deep neural network vulnerabilities by using Adversarial Example.In this method, we add small perturbation to trac which misleads classier to detect websites that the user has visited. In the second defense, we introduce a defense mechanism based on... 

The objective of this investigation was obtaining sound Friction Stir Welded (FSWed) Commercially Purity Titanium using suitable Tool’s Materials (for Shoulder and Pin) in order to be able to work in high temperature (>1000 ˚C) with great mechanical properties and minimum wear during process. Consequently, different materials and designs for Tool, such as High Speed Steel tool, Tungsten based tool, Tungsten Carbide (WC-Co) based tool and diverse tool geometry and designs like simple design, threaded design, fixed pin and inserted pin (adjustable pin) was used. The results demonstrated that using simple cylindrical WC-Co for pin and Tungsten for shoulder resulted in joints with the best... 

Up to now many different mechanisms have been proposed for a swimming micro robot, but most of the previously designed micro robots are not able to perform three- dimensional maneuver and the motion of the proposed swimmers are limited along a straight line or in a plane. Some important issues that must be ruled in designing micro robots include: reduced number of actuators, high maneuverability, high motion controllability and elimination of lateral drift. In this study the aim is to design a micro swimmer with the aforementioned capabilities as much as possible. In this regard, many different ideas based on the quadrotor motion, flagellated bacteria and spiral flagellated bacteria, Fish... 

Some have argued that two-way markets, such as the online rideshar-ing platforms, which divide their services into different segments and provides each of these segments to the independent workforce based on an articulate and transparent income criterion, are more attrac-tive to women, which in turn, can reduce income disparities. This is due to the flexibility in working hours as well as the transparency of the labor payment process. In this study, using micro-data related to the trips of male and female drivers of Tap30, we find out that there is a 2.2 % gender earning gap between drivers. Furthermore, the fac-tors affecting the possible income difference are identified. On the one hand,... 

Water plays an essential role in the daily lives of humans, plants, and animals. Due to the lack of safe water on the planet, in recent years there have been many challenges in the field of water treatment, which has made water desalination technology always one of the most advanced technologies. The most advanced technology in this field is the use of nanotechnology in water and wastewater treatment, especially the use of Membrane processes such as reverse osmosis. Unlike conventional reverse osmosis membranes, nanoporous membranes can ensure rapid water transfer during the displacement process. The purpose of this thesis is to introduce new monolayers that have an incredible performance in... 

In this study, three recent predictors of severity of coronary stenosis including fractional flow reserve (FFR), instantaneous wave free-ratio (iFR) and coronary flow reserve (CFR), are calculated for a number of patient-specific models of left coronary arteries. These patients are admitted to Tehran heart center. The main aim is presenting the optimum numerical and clinical detection technique to assess the severity of coronary stenosis. The effect of geometric features of stenosis is studied on the results of the FFR, iFR, and CFR in order to determine their accuracy. It is observed that CFR does not have a good estimate of the amount of disease. But, iFR, as a less risky test than FFR,... 

In this thesis, we consider multiple-antenna K-user interference channels with backhaul collaboration in one side (among the transmitters or among the receivers) and investigate the trade-off between the rate in the channel versus the communication load in the backhaul. In this investigation, we focus on a first order approximation result, where the rate of the wireless channel is measured by the degrees of freedom (DoF) per user, and the load of the backhaul is measured by the entropy of backhaul messages per user normalized by log of transmit power, at high power regimes. This trade-off is fully characterized for the case of even values of K, and approximately characterized for the case of... 

Lead produced by pyrometallurgy method has a number of impurities. Most of these eimpurities can easily be removed, but this property does not apply in the case of bismuth. Since chemical properties of bismuth are close to the lead, refining of bismuth below 250 ppm is difficult and expensive. Because of problems related to electrochemical discussion of the batteries, bismuth it is possible to reduce below than 20 ppm. Jollivet and Dittmer process is capable of reducing bismuth below 20 ppm. As the main goal of this project is to reduce bismuth to small amounts, Jollivet process was used. Potassium needed for Jollivet process, produced by electrolysis of Potassium chloride salt.... 

The project aims to design and build a device that is capable of manipulation and control of micro-scale objects in dry and fluid medium. Among all the micro-manipulation methods, the use of magnetic fields has many applications. Because it has the ability to work without direct contact and also within a specified range for living tissue, is safe. To achieve this goal,manipulation systems ever made, were studied. Then, by presenting a conceptual design and the use of appropriate dynamic models for describing the behavior of micro-robot, the system performance was simulated. After this stage, The detailed design of the closed-loop system which must controls the position of the micro-robot... 

Because of flexibility in labor supply, ride-sharing market is a good platform for estimating drivers’ working hours in response to hourly earning changes. In this research using ride-sharing markets’ data and controlling for geographic effects and time and individual fixed effects, we have estimated 0.0129 for price elasticity of drivers’ working hours. Literature has focused on estimating the elasticity in time horizons shorter than a day (non-stop active hours), while in this paper we have also estimated the elasticity in daily horizon.We have also analyzed the heterogeneity of different types of drivers (Full-Time or Part-Time, Tehran or non-Tehran Plates, Gender and Experience) in... 

Online ride-hailing platforms aim to match drivers and riders instantly by receiving ride requests from riders and sending them to drivers nearby. However, the low acceptance rate of offers by drivers leads to friction in the process of driver and rider matching. Various factors influence drivers' decisions to accept or reject offers. Specifically, drivers are more likely to turn down a ride offer when they know that by rejecting it, they can quickly receive another offer or find a passenger traditionally. To examine the factors influencing drivers' decisions in online ride-hailing markets, we focus on the behavior of drivers employed by Tapsi ride-hailing platform, and by specifying a... 

In this research, the price effects of freight announcement salons in the road freight transportation market of Iran have been investigated. The road freight market in Iran has witnessed numerous protests by drivers in recent years. One of the main demands of this group was to establish freight salons in terminals lacking that. Contrary to the opinion of drivers, who believe that freight salons increase parity and remove intermediaries, freight companies believe that this policy reduces competition and quality and increases freight prices. In this study, using the information of waybills (“Baarnameh”) at transaction level, we show that the presence of freight announcement salons increases... 

Today, with the development of technology, cyberattacks are on the rise. Personal and corporate computer systems can be exposed to various threats and dangers of hackers and malware, including information theft, forgery, and denial of service, which can cause great material and moral damage to individuals and organizations. So, it is necessary to take security measures in this regard. Many security mechanisms are available to prevent security vulnerabilities against various threats. In this study, first, after carefully studying network attacks, we identify the criteria for identifying attacks that can be executed in network traffic and explain how to calculate them. The current research... 

IC221M is a cast Ni3AI-based intermetallic alloy which chemical composition bases on Ni- 8Al-8Cr-1.5Mo-1Zr-O.OIB %wt. Because of high strength, good high temperature oxidation, carburization and creep resistance as mechanical and physical properties, IC221M has got good attention in aeronautical, military and steel production industries nowadays. The best service temperature range is 600-800°C and melting starts at II 70°C. Since 1993 according to broad range of researches and applications, ASTM standardized it at Al002-99 and from that time researchers try to replace steel with IC221M. %80 volume of microstructure in this alloy consisted of brittle y' and remain are y and low... 

One of the most significant aerial vehicles which has been subject of study of so many engineers and students is quadrotor or quadcopter, which is a cross sectional configuration of motors and propellers. This aerial robot is controlled through slight differences between the angular velocities of the four motors, and robot dynamics is completely nonlinear, thus sophisticated control algorithms are needed. The aim of this project consists of design, fabrication and control of a quadrotor capable of stable hovering. First, some preliminary decisions about general charachteristics of the robot were made. According to these decisions, other mechanical parts were designed and fabricated. Then,...