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    Design of a DDS-Based Frequency Synthesizer for MMW Imaging System

    , M.Sc. Thesis Sharif University of Technology Ghazanfari, Saman (Author) ; Fakharzadeh Jahromi, Mohammad (Supervisor) ; Shabany, Mahdi (Co-Supervisor)
    Abstract
    Nowadays, frequency synthesizers are widely used in many modern devices due to the ever-increasing growth of electronic circuits and their applications in various aspects of life. Imaging devices with security applications in the millimeter-wave frequency band is one of the mentioned applications. To prevent crowds at checkpoints and facilitate traffic, these devices need to monitor people's security at the highest possible speed. Furthermore, significant bandwidth is required to increase image quality. Therefore, using frequency generators with high-speed frequency sweep ability is a great advantage. In this thesis, a digital frequency generating chip with 1GHz bandwidth is designed using... 

    Investigation of the continuum-rarefied flow and isotope separation using a hybrid CFD-DSMC simulation for UF6 in a gas centrifuge

    , Article Annals of Nuclear Energy ; 2020 Ghazanfari, V ; Akbar Salehi, A ; Reza Keshtkar, A ; Mahdi Shadman, M ; Hossein Askari, M ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    UF6 gas flow in the total regions of a rotor with the radius of 0.1 m and the length of 1 m in axisymmetric and steady states was simulated using a new hybrid CFD-DSMC method in the OpenFOAM framework. Implicit coupled density-based scheme was performed for CFD method, and Variable Hard Sphere (VHS) and diffuse model were employed in DSMC method. Also, as an initial estimation, the local Knudsen number was applied to determine the interface location between the continuum-rarefied regions (r = 0.0855 m). Then it was modified (r = 0.084 m) to reduce the computational cost. The comparison results of pure CFD and CFD-DSMC methods illustrated that there were large differences between the flow... 

    Investigation of the continuum-rarefied flow and isotope separation using a hybrid CFD-DSMC simulation for UF6 in a gas centrifuge

    , Article Annals of Nuclear Energy ; Volume 152 , 2021 ; 03064549 (ISSN) Ghazanfari, V ; Akbar Salehi, A ; Reza Keshtkar, A ; Mahdi Shadman, M ; Hossein Askari, M ; Sharif University of Technology
    Elsevier Ltd  2021
    Abstract
    UF6 gas flow in the total regions of a rotor with the radius of 0.1 m and the length of 1 m in axisymmetric and steady states was simulated using a new hybrid CFD-DSMC method in the OpenFOAM framework. Implicit coupled density-based scheme was performed for CFD method, and Variable Hard Sphere (VHS) and diffuse model were employed in DSMC method. Also, as an initial estimation, the local Knudsen number was applied to determine the interface location between the continuum-rarefied regions (r = 0.0855 m). Then it was modified (r = 0.084 m) to reduce the computational cost. The comparison results of pure CFD and CFD-DSMC methods illustrated that there were large differences between the flow... 

    Experimental investigation of water alternating CH4-CO2 mixture gas injection to light oil reservoirs

    , Article 74th European Association of Geoscientists and Engineers Conference and Exhibition 2012 Incorporating SPE EUROPEC 2012: Responsibly Securing Natural Resources, 4 June 2012 through 7 June 2012 ; June , 2012 , Pages 3919-3923 ; 9781629937908 (ISBN) Ghazanfari, M. H. G. H ; Alizadeh, A
    European Association of Geoscientists and Engineers, EAGE  2012
    Abstract
    In this work effect of composition changes of injection gas, CH4 + CO2, on the performance of immiscible WAG injection in light oil, 41 oAPI, which has been rarely attended in the available literature is investigated. Presence of CO2 helps to reduce the MMP of CH4 significantly. Core flood experiments are conducted at reservoir conditions and fixed flow rate of 0.5cc/min on a sandstone sample with the brine concentration of 5000 ppm, and the influence of injection gas composition as well as WAG ratio on oil recovery is investigated. Different mole percents of methane in mixture, 0%, to 100% are examined, and the tests continued to ten alternate cycles with a slug size of 0.1 pore volumes and... 

    MBBR and MBR Reactor Configuration for Better Performance

    , M.Sc. Thesis Sharif University of Technology (Author) ; Borgheei, Mahdi (Supervisor)
    Abstract
    Membrane bioreactors (MBRs) which are commonly understood as the combination of membrane filtration and biological treatment using activated sludge have several advantages, but membrane fouling reduces the membrane efficiency, permeability and lifetime. An alternative is replacing a moving bed biofilm reactor (MBBR) with the activated sludge system which may reduce the effect of membrane fouling. The sludge produced in MBBRs has poor settling characteristics, therefore, their efficiency is limited by the sedimentation tank performance and they require a larger settling surface. The combination of moving bed biofilm reactors and membrane bioreactors can compensate for the drawbacks of both of... 

    Calibration of forming limit diagrams using a modified Marciniak-Kuczynski model and an empirical law

    , Article Materials and Design ; Volume 34 , Feb , 2012 , Pages 185-191 ; 02641275 (ISSN) Ghazanfari, A ; Assempour, A ; Sharif University of Technology
    2012
    Abstract
    The major problem in determining the forming limit diagram (FLD) with the Marciniak-Kuczynski (M-K) model is the necessity of an experimental point in order to find the initial inhomogeneity coefficient and calibrate the diagram. The purpose of the present work is to eliminate this requirement. To do this, the usual assumption of geometrical inhomogeneity has been replaced with material inhomogeneity and it has been shown that the sensitivity of the diagram to variations of the inhomogeneity factor is reduced greatly with the new assumption. Using this advantage and collecting enough experimental data for different materials, an empirical law in terms of sheet thickness has been proposed... 

    A new calibration method for FLCs in the M-K frame-work

    , Article Advanced Materials Research, 8 July 2011 through 11 July 2011 ; Volume 341-342 , July , 2012 , Pages 426-431 ; 10226680 (ISSN) ; 9783037852521 (ISBN) Ghazanfari, A ; Assempour, A ; Sharif University of Technology
    2012
    Abstract
    The main drawback of the method proposed by Marciniak and Kuczynski for prediction of the limit strains in sheet metal forming processes is requirement of an experimental point of the forming limit curve (FLC) in order to calibrate the curve. The purpose of this work is to introduce a new method to calibrate the FLC using the M-K model in which no experimental data is needed. To achieve this goal, many experimental FLCs were collected from the literature and the values of the initial inhomogeneity factors were determined for them with trial and error aproach. Using these data, an empirical law was developed to predict the value of inhomogeneity factor. The resultant curves show good... 

    A critical assessment of forming limit prediction models and beneficial modifications to them

    , Article SAE Technical Papers ; 2012 Ghazanfari, A ; Assempour, A ; Sharif University of Technology
    SAE  2012
    Abstract
    Major forming limit prediction models and calibration methods are reviewed briefly and their advantages and disadvantages are discussed. Two modified Marciniak-Kuczynski (M-K) models and one modified NADDRG (Keeler-Brazier) model are also presented which have some advantages over conventional models. In the first modified M-K model, material non-homogeneity has been substituted for geometrical non-homogeneity to reduce the sensitivity of the traditional model to variations of the initial non-homogeneity. Using this important advantage, a semi-empirical relation is proposed to predict the value of the initial material non-homogeneity. In the second modified M-K model, the conventional... 

    Control of Multi Inverter Microgrid Considering Hybrid Distributed Generation Systems and Renewable Energy Sources in Island Mode

    , M.Sc. Thesis Sharif University of Technology Ghazanfari, Amin (Author) ; Mokhtari, Hossein (Supervisor)
    Abstract
    Nowdays, distributed generation (DG) systems based on renewable energy sources have significantly increased around the world as an alternative solution to enhance the power quality and reliability and reduce the need for extensive transmission system as well. An evolved recent concept called microgrid is developed by grouping a cluster of loads and DG units in a common local area which increases the integaration of sustainable energy generation systems. This thesis presents control of a medium voltage (MV) microgrid considering multi-hybrid distributed generation systems (MHGS) and renewable energy resources in island mode. The first part is focused on the development a control strategy for... 

    A Feedback-based Process of Corporate Structur Design

    , M.Sc. Thesis Sharif University of Technology Ghazanfari, Hossein (Author) ; Modarres, Abdolhamid (Supervisor)
    Abstract
    Designing the structure of organization is one of the most important issues confronting all managers, especially those in large corporations. Structure design process consists of making several trade-offs about parameters that are affected with various contingency factors. This leads manages to confusion so some of them have no plans for progressing this process. Referring to organization theory and design, one sees a large number of models of organizational structure design. But there is not any means to compare them with each other. In this research, next the introduction of a conceptual feed-back model of organizational structure design process, three well-known processes in the last... 

    International Oil Price Time Series Prediction Using GMDH Neural Network and its Performance Comparison with MLP Neural Network and ARIMA Method

    , M.Sc. Thesis Sharif University of Technology Ghazanfari, Mahdi (Author) ; Haji, Alireza (Supervisor)
    Abstract
    Predicting oil prices, especially in exporting countries, will help governments in the policy-making process by obtaining a reliable estimate of oil revenues. The existence of a complex mechanism governing the process of oil price formation has reduced the efficiency of linear models in forecasting and led researchers to use nonlinear intelligent systems to predict oil prices. In this study, after a detailed study of the structure of artificial neural network, two models of neural network GMDH and MLP and ARIMA method have been used to predict oil price. There are important factors in the prediction process with neural networks, and if all these factors are selected correctly; One can expect... 

    Forecasting the effects of a Canada-US currency union on output and prices: A counterfactual analysis

    , Article Journal of Forecasting ; Volume 32, Issue 7 , 2013 , Pages 639-653 ; 02776693 (ISSN) Mahdi Barakchian, S ; Sharif University of Technology
    2013
    Abstract
    This paper is a counterfactual analysis investigating the consequences of the formation of a currency union for Canada and the USA: whether outputs increase and prices decrease if these countries form a currency union. We use a two-country cointegrated model to conduct the counterfactual analysis, where the conditional forecasts are generated based on the Gaussian assumption. To deal with structural breaks and model uncertainty, conditional forecasts are generated from different models/estimation windows and the model-averaging technique is used to combine the forecasts. We also examine the robustness of our results to parameter uncertainty using the wild bootstrap method. The results show... 

    Microwave assisted regeneration of carbonyl compounds from 2,4-dinitrophenylhydrazones with potassium ferrate(VI) supported on montmorillonite K-10

    , Article Acta Chimica Slovenica ; Volume 51, Issue 2 , 2004 , Pages 337-342 ; 13180207 (ISSN) Ghazanfari, D ; Hashemi, M. M ; Sharif University of Technology
    2004
    Abstract
    2,4-Dinitrophenylhydrazones were efficiently and rapidly converted to their corresponding carbonyl compounds with supported potassium ferrate(VI) under microwave irradiation  

    Experimental and Theoretical Investigations of Calibration Methods and Factors Influencing the Forming Limit Diagrams

    , M.Sc. Thesis Sharif University of Technology Ghazanfari, Amir (Author) ; Assempour, Ahmad (Supervisor)
    Abstract
    In designing of sheet metal forming processes, knowledge of the maximum permissible strains in the sheet is of prime importance for the design engineer. Thus, a large amount of experimental and theoretical researches have been carried out to estimate these limiting strains. A renowned and prevalent theoretical method for prediction of forming limits is the Marciniak and Kuczynski model. In this model, it is assumed that a small groove exists in the sheet even before applying the loads; and due to the weakness of this region, necking starts from there. The major problem of the M-K model is requiring of an experimental point to “calibrate” the results. Furthermore, while experiments indicate... 

    Pore-Scale Experimental Study of Foam/Nano-Foam Flooding to Heavy oil in Heterogeneous Five-Spot System: Stability Analysis and Displacement Mechanisms

    , M.Sc. Thesis Sharif University of Technology Suleymani, Mohammad (Author) ; Ghazanfari, Mohammad Hossein (Supervisor)
    Abstract
    Foam injection for enhanced oil recovery is concerned by petroleum engineers because it decreases adverse effects of fingering and gravity segregation caused by the injected fluid .Obviously foam stability is an important factor in the efficiency of this process. So investigating it is an imperative. One of the ways that less studied and can improve foam stability is using of nanoparticles. In this project effect of nanoparticles on foam stability and displacement mechanism during foam flooding has been discussed.
    Study consisted of two sets of experiments. In the first part, the static foam stability in the presence of silica nanoparticles has been investigated. Also influence of... 

    Modeling and Simulation of Miscible Flow through Fractured Porous Media Using Random Walk Method

    , M.Sc. Thesis Sharif University of Technology Fayazi, Amir (Author) ; Ghazanfari, Mohammad Hossein (Supervisor)
    Abstract
    Miscible displacement in fluid flowing through a porous medium plays an important role in many environmental and industrial applications; for instance, miscible displacements in enhanced oil recovery processes and pollutant spreading in groundwater. A large number of numerical approaches have been developed to solve the advection-dispersion equation that describes the behavior of miscible displacement in porous media. Most of these numerical models suffer from numerical dispersion. Random walk seems to be an effective method to overcome this problem especially in heterogeneous media. Here, a random walk model was developed and used for simulating miscible displacement in heterogeneous porous... 

    Evaluation of Non-linear Combination Method (Neural Network) For Value-at-Risk Forecasting in Market

    , M.Sc. Thesis Sharif University of Technology Rashnavadi, Leila (Author) ; Barakchian, Mahdi (Supervisor)
    Abstract
    Value at risk of an asset, is the asset’s expected maximum loss for a certain period of time and at a specified confidence level. Value-at-Risk can be calculated in the bank with its inter-nal method or standardized method. when a method have more violation number then bank need to keep more daily capital requirements. under the Basel 2 agreement if the violation of method more than 10 times in year, the Bank uses the standardized method.
    There are trade off Between daily capital charge and violations. Therefore, existing methods for calculating the value at risk, usually lead to much daily capital charge or many violations. Studies show with combination of different methods to calculate... 

    Using Complex Network Metrics for Evaluating the Influence of Conference and Journal Papers in Computer Science

    , M.Sc. Thesis Sharif University of Technology Habibi, Fatemeh (Author) ; Jalili, Mahdi (Supervisor)
    Abstract
    Journals and conferences in computer science are the major venue for publishing new achievement in the field. It is an expert opinion that a number of top conferences in computer science are even more important than journals. In this work we aim at studying this in terms of citation analysis. To this end, we took 100 top journals and 63 top conferences and extracted their citation graph through Scopus dataset. We then constructed the citation graph in which the nodes were the journals and conferences and the links corresponded to the citations of the papers. We used various measures to rank the nodes in the graph. The ranking methods included Prestige, PageRank, Eigenfactor, HITS and SALSA.... 

    Design and Implementation of a VLSI Architecture for Time and Frequency Synchronization in the LTE

    , M.Sc. Thesis Sharif University of Technology Golnari, Amene (Author) ; Shabany, Mahdi (Supervisor)
    Abstract
    The long term evolution (LTE) standard is introduced and developed by the 3rd generation partnership project (3GPP) based on orthogonal frequency division multiplexing (OFDM). OFDM systems, in spite of having many advantages such high performance in bandwidth usage, are very sensitive to inter carrier interference (ICI) as a drawback. In order to prevent ICI, the frequency offset, mainly caused by the miss-match between oscillators' frequency and also between the sampling frequency of the transmitter and the receiver, should be estimated and compensated. Frequency synchronization is a part of the tasks of a synchronizer. In this thesis, main tasks of a synchronizer are illustrated and... 

    A New Approach in Value-at-Risk (VaR) Estimation by Forecast Combination Methods

    , M.Sc. Thesis Sharif University of Technology Seraj, Mostafa (Author) ; Barakchian, Mahdi (Supervisor)
    Abstract
    Value-at-Risk (VaR) is the most commontool for risk management. This tool is used to measure market risk and also used as a basis in determining financial standards for international financial institutions. VaR is the maximum loss of the asset portfolio at the specified confidence level and certain time horizon. Many parametric, nonparametric and semi parametric methods have been invented for VaR estimation. Each one of these methods has its advantages and disadvantages and different methods may perform better in differnet situations.When estimating VaR, we can choose one of these methods or we can combine the VaRs estimated by different methods. There are few researches conducted on VaR...