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... 

Statistical studies indicate the fact that in Iran, like many other developing countries, a significant percentage of buildings are made of traditional materials and most of them are adobe buildings especially in rural areas. Furthermore, geological data indicates that Iran is located in alps-Himalayas seismic zone and exposed by destructive earthquakes and adobe buildings suffer the most damages comparing with other type of the structures. According to these explanations, this research deals with adobe buildings behavior and provides solutions for reinforcing them and improving the seismic response of these buildings. These studies include numerical modeling with finite elements methods by... 

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... 

In this thesis we consider the problem of distributed computation by many processors.We mainly concentrate on matrix multiplication problem in this thesis because of its importance. A distributed system consists of N worker processors and one master processor. The master processor should distribute the computation between workers and after computation in each of them, collect the results. In this thesis, we are going to mitigate the effect of straggler processors by using coding methods. Straggler processors can cause delays in the computation time.In this thesis, we firstly introduce a method to multiply any number of matrices in each other. The proposed method occurred in one shot without... 

The main goal of current investigation was partial reduction of Fe2O3 available in Hematite-rich ore to Magnetite by Fludization Bed method. The reductive gas, CO, was produced by incomplete combustion of Acetylene and Airmixed in inappropriate ratio. X-Ray Diffraction and X-Ray Florescence analyses were implemented in order to conducting qualitative analysis of present phases before and after reduction of the ore. Quantitative analysis of the same phases was also conducted by Titration. The latter analysis revealed the precise magnitude of available iron in each of the oxide containing phases. The chemical composition of the reactor gas was also determined before and after reduction... 

Abstract The problem of competetive facility location can be defined as follows: There are a number of customers in the form of points in space, and two players arrange a number of facilities in the form of points in space, given some limitations, respectively. Each customer’s connection to each facility has a cost for the customer and an advantage for the facility, and each customer wants to be connected to at most one of the facilities which has the lowest cost for him. The goal is to find the strategy of placing the facilities and determining the cost which the facility receives from the customer, in such a way that the player’s profit is maximised.In this thesis, we first sought to... 

Zero knowledge proofs allow a person (prover) to convince another person (verifier) that he has performed a specific computation on a secret data correctly, and has obtained a true answer, without having to disclose the secret data. QAP (Quadratic Arithmetic Program) based zkSNARKs (zero knowledge Succinct Non-interactive Argument of Knowledge) are a type of zero knowledge proof. They have several properties that make them attractive in practice, e.g. verifier's work is very easy. So they are used in many areas such as Blockchain and cloud computing. But yet prover's work in QAP based zkSNARKs is heavy, therefore, it may not be possible for a prover with limited processing resource to run... 

Lightweight clients are a type of blockchain users who do not store all the blocks in the blockchain due to limited resources. These users store only a small part of each block and when needed, request transactions from full nodes that store the entire blockchain. These users have no role in block validation and only want to receive transactions related to their addresses with proof of the inclusion in the block from full nodes.Since light clients rely on full nodes for receiving transactions, their privacy against full nodes is important. The current implementation of Bitcoin uses Bloom filters for privacy, but this offers very little privacy to the users.In this thesis, we study the...