Sharif Digital Repository

The PTC effect which is one of the most important properties of electroceramics is being used in lots of electrical devices. This effect is observed in ceramics based on Barium Titanate. In the present study, the effects of grain size and two-step sintering method on PTC effect of Barium Titanate were investigated and La2O3 was used as an additive to improve the PTC effect and sintering behaviors of BaTiO3. Characterization analysis showed that the BaTiO3 powders had Cubic structure up to 700°C and Tetragonal structure at 1150°C. The FE-SEM analysis and density analysis showed that the samples which were two-step sintered at T1 less than 1200°C only reached 90% of relative density. Under... 

In Iran, the Iranian Nuclear Waste Management Company (INWMC) is responsible for safe disposal of low-level radioactive waste which results from different processes of nuclear fuel cycle and other radioactive-related activities. The safety assessment program is essential to ensure safe isolation of radioactive waste from the biosphere for long periods of time. Usually, the ground water scenario is considered as the main scenario of radionuclides migration from repository to the biological environment. Thus, it is required to measure the transport parameters of radionuclides in the porous media (soil) around the disposal site. In this research, laboratory scale columns, filled with Nain... 

This research presents an innovative analytical solution to static, free vibration and buckling of an isotropic, homogeneous Mindlin plate with uniform thickness. This method satisfies all classical boundary conditions including free, simply supported and clamped as well as non-classical ones. Moreover, Mindlin plates on Winkler foundation of arbitrary stiffness function are investigated. In this study, the deflection and rotation of straight normal line of the plate about x and y axes are represented as the functions of sine and cosine Fourier series, accompanied by auxiliary functions. These auxiliary functions are of great importance because these functions satisfy arbitrary boundary... 

The phenomenon of dynamic stall is one of the major challenges in aerodynamic engineering, significantly affecting the performance, stability, and efficiency of flight systems such as helicopters and rotorcraft. In this study, a nanosecond dielectric barrier discharge (NS-DBD) plasma actuator is employed as a novel method for active flow excitation and separation delay to control this phenomenon. The main objective of this research is to develop a novel feature-based subgrid modeling approach for the NS-DBD actuator, capable of representing the effects of its electrical and geometrical characteristics—including coupled energy, plasma thickness and length, heating duration, and gap... 

In the recent years, the world has been faced with a spectacular increase in variety and usage of electronic and electric devices. Unfortunately, the highly increasing march of technology reduces the time of their usage, causing a high degree of electric and electronic waste. Nonetheless, these E-waste enjoys a high percentage in precious metals such as Cadmium, Copper, Nickle, Zinc, Barium, Beryllium, Aluminum, Gold, Silver, Platinum, and so forth. With this in mind, they can be named as “secondary mines”, enjoying higher in degree of these metals even than natural mines. Therefore, extraction and recovery of the very metals are of great importance. Nowadays, using microorganisms in order... 

In this research, the issue of outsourcing control calculations to servers or external computing parties for non-ideal situations has been discussed. Due to the confidentiality of the information of the control systems, it is necessary to guarantee and maintain the privacy of the data from sensors to the actuators. In this research, secure multi-party computation using secret sharing has been utilized to establish the privacy of these data and simultaneously outsource control computing. In other words, the goal is to design a secure controller by means of secure multi-party computations. One of the most important challenges in the design of controllers that use communication channels to send... 

Microfluidics is an emerging technology that has attracted lots of attention in recent years due to its remarkable capabilities. This technology that operates fluids in micron dimensions, has led to the emergence of lab-on-a-chip platforms that have the ability to perform one or more laboratory operations on a small scale. One of the most important applications of lab-on-a-chip devices is cell sorting which is done in various methods. In this study, we intend to provide a simple and practical solution for cell sorting by designing a comprehensive and optimized system. In this regard, we design a new generation of microfluidic devices, known as digital microfluidics, which has the ability to... 

In this study, various methods of speech time scale modification are inspected and the most important one is modified. First, a brief review on all existing methods for audio time scale modification and its applications is presented in introduction section. As will be noted, the presented method could be classified in three classes of Time domain, Phase-vocoder and signal model. In next chapter a review on Time-domain methods is presented and its advantages and disadvantages have been addressed. Afterward, a review on Phase-vocoder and Signal-model methods is expressed in chapter 3 and 4 respectively. Considering the complexity and extent material relating to these techniques, the research... 

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... 

High entropy oxides are a group of oxides which consist of five cations and are stable at high temperature. Since these materials have unique properties such as high ionic media, high capacity and cycle stability, they can be considered for use in lithium-ion batteries. In this regard, in this research, for the first time, the effect of vanadium element in oxide with high entropy for use as anode in lithium-ion battery has been investigated. Therefore, (VCrMnNiCo)3O4 high entropy oxide has been synthesized by hydrothermal method and then the single-phase structure has been stabilized at 900°C. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) studies have... 

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... 

We discuss and classify all four dimensional black hole solutions to Einstein-Maxwell-Lambda theory. These solutions contain a black hole region with an event horizon. The cosmological constant can be nonzero and the black hole may possess electric and magnetic charge. We classify solutions according to their asymptotic behavior. Three major parts are asymptotic-flat, asymptotic-de Sitter and asymptotic-Anti-de Sitter and in all of them we discuss Schwarzschild, Reissner-Nordstrom, Kerr and Kerr-Newman black holes separately. Black holes can also have NUT charge and acceleration parameter which make the solution singular in one direction. As a result, these solutions are asymptotically... 

Power system frequency regulation entitled load frequency control (LFC) has been one of the important control problems in electric power system design and operation. Off-normal frequency can directly impact on power system operation and system reliability. A large frequency deviation can damage equipment, degrade load performance, cause the transmission lines to be overloaded and can interfere with system protection schemes, ultimately leading to an unstable condition for the power system . On the other hand, the increasing need for electrical energy in the 21st century, as well as limited fossil fuel reserves and the increasing concerns with environmental issues for the reduction of carbon...