Sharif Digital Repository

Since robustness of peer-to-peer networks depends heavily on voluntary resource sharing among individual peers, the intrinsic problem of free riding exists among autonomous rational peers that consume resources of others without contributing anything in return. One solution to the free riding problem in peer to peer networks is to have incentive mechanisms that aim to improve network efficiency by encouraging peers to cooperate. In this project, we have proposed a hybrid double-auction-based incentive mechanism for centralized peer-to-peer file sharing systems. In addition, a cryptography-based trust management scheme has been proposed to prevent peers from sending fake data. We have... 

Liquefaction is one of the probable consequences of earthquake in soil layers of saturated loose sands. Various aspects of liquefaction have been investigated using different methods of field, laboratory, and numerical studies. Numerical simulation of liquefaction constitutes a major part of these researches. A proper constitutive law must be implemented in the numerical analysis for modeling the complicated behavior of saturated sands during dynamic loading. Simplicity of formulation, limited number of parameters and good performance are the main features of a proper constitutive law. In this study, Endochronic model for simulating liquefaction has been introduced. This model is implemented... 

In this study, a fully coupled three-dimensional numerical analysis of two-phase fluid flow and heat transfer through deformable porous media is presented in the context of extended element free Galerkin method. By coupling momentum balance equation for the whole mixture, continuity equations of wetting and non-wetting fluid phases and energy balance equation, the developed numerical algorithm is capable of simulating a wide range of engineering problems such as CO2 sequestration, nuclear waste disposal in deep underground strata, hydraulic fracturing in oil and gas reservoirs and so on.By taking the advantages of partition of unity property of MLS shape functions, weak and strong... 

The popularity of Internet-based video services has increased in recent years, while in 2017 reached nearly 70% of the total Internet traffic. Changes in network status and the problems that result in the user experience leading to poor quality of the video watching experience, online video players have been using adaptive algorithms to match the quality of the received stream to the current state of the network. Different algorithms have been proposed for optimization of matching operations, but due to the different and sometimes contradictory nature of the constituents of the quality of user experience, the priority and focus of each of these algorithms is based on different challenges... 

Despite eye-catching progressive trends in highway safety, there have been a great number of unpleasant incidents in highways. A number of 8841 people died in road accidents in the first 6 month this year with 1.7% increase compared to the accidents occurred in 1396 [59]. Operation of a modeling process shall provide the engineers with more opportunities to identify the affecting factors in roads incidents. Safety infrastructure management is mainly aimed at ensuring the efficient measurement, systematic recognition and consequently deterioration of road accidents when they have been designed, constructed and used [37]. Building information modeling (BIM) tends to be a developed managerial... 

Sign Language Recognition using cameras is an alternative way of human communication with personal computers. These systems don’t need to use keyboard. They are used when touching keyboard is not possible or for what ever reason, when we don’t want to use keyboard. In this problem the person shows one of the alphabets with his hand and we capture and process that in real-time to recognize the letter. The problem of previous works in this area are the decreasing rate of detection in condition where the angle of sign and viewer changes. The purpose of our work is getting better result by using depth image from Kinect. We use Pugeault and Bowden dataset (that has fingerspelling sign in multiple... 

The primary purpose of acidizing operations in the oil and gas industry is to enhance hydrocarbon production. Acidizing has been a common and conventional method for years, especially when production engineers face issues like declining reservoir pressure leading to reduced production rates. Initially, the treatment solution is referred to as matrix acidizing. In acidizing operations, different additives are combined with the acid to control its behavior in the reservoir. These additives may include iron control agents, corrosion inhibitors, friction reducers, and more. Incompatibility among these additives, the acid, and reservoir fluids can lead to severe damage to the reservoir.... 

The goal of this research is the simulation of the annular combustion chamber of the turbine engine utilized by liquid fuel. The achievement to this goal will lead to create numerical tools for parametric study, analysis and combustion chamber designing.For this reason simple geometry has been considered. This simplicity of geometry causes to facilitate in parametric study and decrease in saving time for modeling and meshing. This combustion chamber is a simplified model of engine CF6. In recent study, the k – ε realizable model has been used for turbulence modeling. For non-adiabatic condition, chemical reaction is dissolved by utilizing probability density function along with laminar...