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    Experimental Investigation of Fretting Fatigue of Titanium Specimens Made by Additive Manufacturing Method

    , M.Sc. Thesis Sharif University of Technology Sajjad Houshmand (Author) ; Adibnazari, Saeed (Supervisor)
    Abstract
    Additive manufacturing (AM) has gained significant attention in recent years as a novel approach to fabricate three-dimensional parts. Its advantages, including high speed, low-cost production for small-scale batches, and greater design freedom, have made it a competitive alternative to traditional manufacturing methods. However, the application of AM for components subjected to fretting fatigue requires careful evaluation. Fretting fatigue is a major cause of failure in turbines, particularly at the contact interface between turbine blade roots and disk. In this study, the influence of AM and post-processing treatments on the fretting fatigue life of Ti-6Al-4V alloy was investigated. Five... 

    Analytical Investigation and Evaluation of Vulnerability of Deep Networks to Adversarial Perturbations

    , M.Sc. Thesis Sharif University of Technology Azizi, Shayan (Author) ; Ghaemmaghami, Shahrokh (Supervisor) ; Amini, Sajjad (Co-Supervisor)
    Abstract
    One of the most important problems in machine learning is investigating the performance of the learning algorithms, and especially deep neural networks, on adversarial examples, which are generated by imperceptibly perturbing input images, so that cause the model make a wrong prediction. Not only this line of research is important for making deep neural networks dependable, but also can help with understanding the fundamental limitations of deep neural networks, and the nature of their operation, which can in turn provide researchers with valuable insights into artificial intelligence. In this research work, we have tried to approach the topic with a mainly theoretical mindset. The method we... 

    Face Forgery Detection Through Statistical Analysis and Local Correlation Investigation

    , M.Sc. Thesis Sharif University of Technology Asasi, Sobhan (Author) ; Ghaemmaghami, Shahrokh (Supervisor) ; Amini, Sajjad (Supervisor)
    Abstract
    Existing face forgery detection methods mainly focus on certain features of images, such as features related to image noise, local textures or frequency statistics of images for forgery detection. This makes the extracted representations and the final decision depend on the data in the database and makes it difficult to detect forgery with unknown manipulation methods. Solving this challenge, which is called the generalization challenge in artificial intelligence literature, has become the main goal of researchers in this field. In this thesis, the focus is on extracting effective features for success in forgery detection and preventing the performance of the forgery detection network from... 

    Robustification of Deep Learning Structures Based Ongenerative Models

    , M.Sc. Thesis Sharif University of Technology Haji Mohammadi, Reza (Author) ; Kazemi, Reza (Supervisor) ; Amini, Sajjad (Supervisor)
    Abstract
    In recent years, deep learning has experienced rapid and remarkable advancements, demonstrating exceptional performance in various applications such as computer vision, natural language processing, and autonomous vehicles. These models are continually evolving and expanding, yet they harbor inherent vulnerabilities that prevent complete trust in their reliability. One of the most critical issues is their susceptibility to adversarial attacks, where a clean image is subtly manipulated to create an adversarial example. Adversarial examples, generated by adding imperceptible perturbations to input data, can easily mislead deep learning models into making highly confident yet incorrect... 

    Analysis and Enhancement of Low Voltage Ride Through Of Wind Turbines with Brushless Doubly Fed Induction Generator

    , Ph.D. Dissertation Sharif University of Technology Gholizadeh, Mahyar (Author) ; Oraee Mirzamani, Hashem (Supervisor) ; Tohidi, Sajjad (Co-Advisor)
    Abstract
    Wind energy technologies guarantee low pollution and operational costs. Using a DFIG and a fractionally rated power electronics converter gives variable speed operation with a low cost drive train. As energy policy organizations have allocated a considerable quota of wind energy generation to offshore wind farms, the absence of slip rings and brushes in the brushless DFIG (BDFIG) is an advantage for offshore wind turbines where maintenance is vital and expensive. With increasing wind power penetration in power systems, grid code requirements are an important consideration for the ride-through capability of wind farms through voltage dips, particularly for multi- MW wind turbine generators.... 

    Optical bistability in fiber ring resonator containing an erbium doped fiber amplifier and quantum dot doped fiber saturable absorber

    , Article Applied Optics ; Volume 51, Issue 29 , 2012 , Pages 7016-7024 ; 1559128X (ISSN) Tofighi, S ; Farshemi, S. S ; Sajjad, B ; Shahshahani, F ; Bahrampour, A. R ; Sharif University of Technology
    2012
    Abstract
    In this paper we study the optical bistability in a double coupler fiber ring resonator which consists of an erbium doped fiber amplifier (EDFA) in half part of the fiber ring and a quantum dot doped fiber (QDF) saturable absorber in the other half. The bistability is provided by the QDF section of the ring resonator. The EDFA is employed to reduce the switching power. The transmitted and reflected bistability characteristics are investigated. It is shown that the switching power for this new bistable device is less than 10 mW  

    Modeling and analysis of the dynamic response of an off-grid synchronous generator driven micro hydro power system

    , Article International Journal of Renewable Energy Development ; Volume 10, Issue 2 , 2021 , Pages 373-384 ; 22524940 (ISSN) Ali, W ; Farooq, H ; Rasool, A ; Sajjad, I. A ; Zhenhua, C ; Ning, L ; Sharif University of Technology
    Diponegoro university Indonesia - Center of Biomass and Renewable Energy (CBIORE)  2021
    Abstract
    This paper models and analyses the dynamic response of a synchronous generator driven off-grid micro hydro power system using Simulink tool of MATLAB software. The results are assessed from various perspectives including regulation through no load to full load and overload scenarios under normal and abnormal operating conditions. The investigation under the normal conditions of no load, linearly changing load and full load divulges that the system operates in a satisfactory manner as generator voltage and frequency remain approximately constant at 1 pu. However, at full load generator voltage and frequency drop 3% and 0.5% respectively from its nominal values but remain within prescribed... 

    Modeling and analysis of the dynamic response of an off-grid synchronous generator driven micro hydro power system

    , Article International Journal of Renewable Energy Development ; Volume 10, Issue 2 , 2021 , Pages 373-384 ; 22524940 (ISSN) Ali, W ; Farooq, H ; Rasool, A ; Sajjad, I. A ; Zhenhua, C ; Ning, L ; Sharif University of Technology
    Diponegoro university Indonesia - Center of Biomass and Renewable Energy (CBIORE)  2021
    Abstract
    This paper models and analyses the dynamic response of a synchronous generator driven off-grid micro hydro power system using Simulink tool of MATLAB software. The results are assessed from various perspectives including regulation through no load to full load and overload scenarios under normal and abnormal operating conditions. The investigation under the normal conditions of no load, linearly changing load and full load divulges that the system operates in a satisfactory manner as generator voltage and frequency remain approximately constant at 1 pu. However, at full load generator voltage and frequency drop 3% and 0.5% respectively from its nominal values but remain within prescribed... 

    Global drag-induced instabilities in protoplanetary disks

    , Article Astrophysical Journal ; Volume 772, Issue 1 , 2013 ; 0004637X (ISSN) Jalali, M. A ; Sharif University of Technology
    2013
    Abstract
    We use the Fokker-Planck equation and model the dispersive dynamics of solid particles in annular protoplanetary disks whose gas component is more massive than the particle phase. We model particle-gas interactions as hard sphere collisions, determine the functional form of diffusion coefficients, and show the existence of two global unstable modes in the particle phase. These modes have spiral patterns with the azimuthal wavenumber m = 1 and rotate slowly. We show that in ring-shaped disks, the phase-space density of solid particles increases linearly in time toward an accumulation point near the location of pressure maximum, while instabilities grow exponentially. Therefore, planetesimals... 

    Finite element modelling of perturbed stellar systems

    , Article Monthly Notices of the Royal Astronomical Society ; Volume 404, Issue 3 , Jan , 2010 , Pages 1519-1528 ; 00358711 (ISSN) Jalali, M. A ; Sharif University of Technology
    2010
    Abstract
    I formulate a general finite element method (FEM) for self-gravitating stellar systems. I split the configuration space to finite elements, and express the potential and density functions over each element in terms of their nodal values and suitable interpolating functions. General expressions are then introduced for the Hamiltonian and phase-space distribution functions of the stars that visit a given element. Using the weighted residual form of Poisson's equation, I derive the Galerkin projection of the perturbed collisionless Boltzmann equation, and assemble the global evolutionary equations of nodal distribution functions. The FEM is highly adaptable to all kinds of potential and density... 

    Chemometrical modeling of electrophoretic mobilities in capillary electrophoresis

    , Article Chemometric Methods in Capillary Electrophoresis ; 2009 , Pages 323-343 ; 9780470393291 (ISBN) Jalali Heravi, M ; Sharif University of Technology
    John Wiley & Sons, Inc  2009

    Unstable disk galaxies. I. Modal properties

    , Article Astrophysical Journal ; Volume 669, Issue 1 , 2007 , Pages 218-231 ; 0004637X (ISSN) Jalali, M. A ; Sharif University of Technology
    Institute of Physics Publishing  2007
    Abstract
    I utilize the Petrov-Galerkin formulation and develop a new method for solving the unsteady collisionless Boltzmann equation in both the linear and nonlinear regimes. In the first-order approximation, the method reduces to a linear eigen-value problem which is solved using standard numerical methods. I apply the method to the dynamics of a model stellar disk which is embedded in the field of a soft-centered logarithmic potential. The outcome is the full spectrum of eigen-frequencies and their conjugate normal modes for prescribed azimuthal wavenumbers. The results show that the fundamental bar mode is isolated in the frequency space, while spiral modes belong to discrete families that... 

    Neural networks in analytical chemistry

    , Article Methods in Molecular Biology ; Volume 458 , 2008 , Pages 81-121 ; 10643745 (ISSN); 9781588297181 (ISBN) Jalali-Heravi, M ; Sharif University of Technology
    2008
    Abstract
    This chapter covers a part of the spectrum of neural-network uses in analytical chemistry. Different architectures of neural networks are described briefly. The chapter focuses on the development of three-layer artificial neural network for modeling the anti-HIV activity of the HETP derivatives and activity parameters (pIC 50) of heparanase inhibitors. The use of a genetic algorithm-kernel partial least squares algorithm combined with an artificial neural network (GA-KPLS-ANN) is described for predicting the activities of a series of aromatic sulfonamides. The retention behavior of terpenes and volatile organic compounds and predicting the response surface of different detection systems are... 

    Unstable disk galaxies. II. the origin of growing and stationary modes

    , Article Astrophysical Journal ; Volume 689, Issue 1 , 2008 , Pages 134-147 ; 0004637X (ISSN) Jalali, M. A ; Sharif University of Technology
    Institute of Physics Publishing  2008
    Abstract
    I decompose the unstable growing modes of stellar disks to their Fourier components and present the physical mechanism of instabilities in the context of resonances. When the equilibrium distribution function is a nonunifonn function of the orbital angular momentum, the capture of stars into the corotation resonance imbalances the disk angular momentum and triggers growing bar and spiral modes. The stellar disk can then recover its angular momentum balance through the response of nonresonant stars. I carry out a complete analysis of orbital structure corresponding to each Fourier component in the radial angle and present a mathematical condition for the occurrence of van Kampen modes, which... 

    Optimal resource allocation for MC-NOMA in SWIPT-enabled networks

    , Article IEEE Communications Letters ; Volume 24, Issue 10 , 23 June , 2020 , Pages 2250-2254 Jalali, J ; Khalili, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    Abstract
    In this letter, we study a receiver architecture technique for joint resource allocation in a downlink (DL) multi-user multi-carrier non-orthogonal multiple access (MC-NOMA) network with simultaneous wireless information and power transfer (SWIPT). In this framework, the subcarrier set is partitioned into two groups that are assigned to perform information decoding (ID) and energy harvesting (EH) at the receiver side based on the optimization problem. This letter seeks to maximize energy harvesting while meeting a minimum data-rate requirement for each user. The underlying optimization problem is mixed-integer non-linear programming (MINLP). To that end, we employ the monotonic optimization... 

    Diffusion of Lipid and Protein Molecules in Cell Membranes

    , Ph.D. Dissertation Sharif University of Technology Khoshnood, Atefeh (Author) ; Jalali, Abbas (Supervisor)
    Abstract
    Lipid membranes are fundamental constituents of cell membranes and are now used in lap-on-a-chip technology. Membranes in living cells contain a significant fraction of proteins, which undergo lateral random movements due to thermal fluctuations and shear forces imposed by the solvent fluid. Prominent natural and biotechnological systems where membranes are highly sheared include the plasma membrane of endothelial cells, and membranes used in biosensors for high throughput screening of drug candidates, and in water purification devices. In these systems membrane is in direct contact with the mainstream suspension flow, which is driven by pressure gradients. The efficiency and function of... 

    Design and Implement of an Ultra Low Ripple Power Supply for Cathode of Microwave Tube

    , M.Sc. Thesis Sharif University of Technology Jalali, Saeed (Author) ; Kaboli, Shahryar (Supervisor)
    Abstract
    The purpose of this Thesis is designing and constructing of high voltage power supply with very low ripple. Proposed method of this thesis is formed of two sections. In this proposed structure, in first section, structure is on basis of diodes rectifier that has been used for producing main portion of output load energy. Second section uses with aim of regulating of first stage voltage. In attention to existence of noises and available offsets in different sections of proposed circuits, model is basis of two stages structure. Sampling of output voltage by using of resistance divider for main loop of circuit has been done. So noises and offsets available in circuit act as prevented factor... 

    The Effect of Wind Turbine Rotor Deflection on Its Aerodynamic Performance Using Actuator Disc Model

    , M.Sc. Thesis Sharif University of Technology Jalali, Ramin (Author) ; Darbandi, Masoud (Supervisor)
    Abstract
    An aerodynamical model for studying asymmetric and three-dimensional flow fields about wind turbine rotors is presented. The developed algorithm combines a asymmetric and three-dimensional Navier-Stokes solver with a so-called actuator disc technique in which the loading is distributed along lines representing the blade forces. The loading is determined iteratively using a bladeelement approach and tabulated airfoil data. Computations are carried out for a 5MW NREL wind turbine equipped with three blades. The computed power production is found to be in good agreement with measurements. The computations give detailed information about basic features of wind turbine wakes, including... 

    Investigation of Strength and Rotation Capacity of Box Column

    , M.Sc. Thesis Sharif University of Technology Jalali, Reza (Author) ; Moghaddam, Hassan (Supervisor)
    Abstract
    In this study, the behavior of box column subjected to constant axial load with cyclic lateral force have been investigated by Finite Element method. The resulf of FE anslysis are in a good agreement with experimental result in predicting of behavior and performance of box column. In order to investigation of behavior uses of some performance indices such as axial shortening, over strength, plastic hinge length, out of plane deformation and rotation capacity. The effect of significant parameter such as axial force to yield strength ratio, flange whidth to thickness ratio of flange, web whith to thickness ratio of web, global slenderness ratio and loading protocol on performance indices have... 

    Upgrading and Developing The Performance of One of the Gas Turbine Engine Secondary air System Components using CFD

    , Ph.D. Dissertation Sharif University of Technology Jalali, Ramin (Author) ; Darbandi, Masoud (Supervisor)
    Abstract
    Numerical three-dimensional simulation of the entire regions of a gas turbine blade, including hot gas flow over the blade surface, conduction heat transfer within the blade metal, and coolant flow through the Internal cooling System, is highly time-consuming and expensive. Therefore, one-dimensional internal flow simulation is one of the main objectives of this research to address the limitations of commercial software in predicting the temperature distribution along the cooling path. In this study, a one-dimensional in-house simulation code is developed to simulate the coolant flow inside the cooling channels of the internal cooling system of the blade. Additionally, using artificial...