Search for: karimi-mahabadi--rayehe
0.121 seconds

    Effects of resonator geometry and substrate stiffness on the tunability of a deformable microwave metasurface

    , Article AEU - International Journal of Electronics and Communications ; Volume 146 , 2022 ; 14348411 (ISSN) Karimi Mahabadi, R ; Goudarzi, T ; Fleury, R ; Sohrabpour, S ; Naghdabadi, R ; Sharif University of Technology
    Elsevier GmbH  2022
    Abstract
    Tunable metasurfaces can shift their resonant frequency through different approaches, one of which is applying mechanical deformations. Here, we show the effects of two key factors on the tunability of deformable metasurfaces; the resonator geometry and substrate stiffness. To show the effects, we compared the tunability of unit cells with three resonator geometries and three common substrates at microwave frequencies from 1 GHz to 10 GHz under a given mechanical deformation. We showed that the resonator geometry affects the deformation field, as a consequence, causes different resonant frequency shifts. Moreover, it affects the stress field in the metasurface which in turn limits the... 

    Effect of mechanical nonlinearity on the electromagnetic response of a microwave tunable metamaterial

    , Article Journal of Physics D: Applied Physics ; Volume 55, Issue 20 , 2022 ; 00223727 (ISSN) Karimi Mahabadi, R ; Goudarzi, T ; Fleury, R ; Orazbayev, B ; Naghdabadi, R ; Sharif University of Technology
    IOP Publishing Ltd  2022
    Abstract
    Tunable metamaterials functionalities change in response to external stimuli. Mechanical deformation is known to be an efficient approach to tune the electromagnetic response of a deformable metamaterial. However, in the case of large mechanical deformations, which are usually required to fully exploit the potential of the tunable metamaterials, the linear elastic mechanical analysis is no longer suitable. Nevertheless, nonlinear mechanical analysis is missing in the studies of mechanically tunable metamaterials. In this paper, we study the importance of considering nonlinearity in mechanical behavior when analyzing the response of a deformable metamaterial and its effects on electromagnetic... 

    Multiscale Multiphysics Analysis of Deformable Microwave Metasurfaces Under Large Deformations and Prototype Fabrication

    , Ph.D. Dissertation Sharif University of Technology Karimi Mahabadi, Rayehe (Author) ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor) ; Goudarzi, Taha (Co-Supervisor)
    Abstract
    Electromagnetic metamaterials are designed artificial materials with sub-wavelength resonant inclusions. They can exhibit extraordinary properties such as negative permittivity, negative permeability, and anomalous reflection/refraction. Metasurfaces are 2D counterparts of metamaterials. Here, we proposed a framework for the multiscale multiphysics analysis of deformable metasurfaces. Nonlinear mechanical analysis (Geometry and material behavior), periodic boundary conditions, homogenization, multiscale analysis, and electromagnetic analysis are implemented in this framework. Benefiting from the framework, we proposed a multifunctional hyperelastic structured surface that can generate... 

    Common Areas of Language Impairment in Persian-speaking Autistic Children

    , M.Sc. Thesis Sharif University of Technology Mahabadi, Sara (Author) ; Khosravizadeh, Parvaneh (Supervisor)
    Abstract
    In qualitative content analysis research with the aim of identifying areas of language impairmenthigh-functioning Persian-speaking autistic children, ten subjects were observed during fifteen training sessions which were the cognitive block of a three-block training program. Each session lasted 90 minutes and was video recorded. Prior to this, focus group interviews with specialists and semi-structured interviews with mothers and parallel to that focus group interviews with mothers were handled all of which were audio recorded. After two levels of initial and second coding, a final list of areas of impairment in the language of high-functioning Persian-speaking autistic children, that... 

    Investigating the Behaviour of Some Kind of Fibre-reinforced Concrete

    , M.Sc. Thesis Sharif University of Technology Alaei Mahabadi, Alireza (Author) ; Khonsari, Vahid (Supervisor)
    Abstract
    While there are many advantages associated with concrete, including high compressive strength, durability and so forth, on the contrary, it has several disadvantages which may make engineers somewhat reluctant to use it. These include low tensile strength, high brittleness, low resistance to impact, large dimensions of structural cross sections, etc. In recent years, there have been many attempts to surmount these disadvantages by various means such as adding pozzolans, using FRPs, fibres, etc. In this project, the effects of using a special type of high strength steel fibre is studied. In order to investigate the effect of this fibre on the compressive behavior of concrete, 30 cylindrical... 

    Improving Robustness of Deep Neural Networks Against Adversarial Examples in Image

    , M.Sc. Thesis Sharif University of Technology Mahabadi Mohamadi, Mohamad (Author) ; Kasaei, Shohreh (Supervisor)
    Abstract
    Despite widespread applications and high performance of deep neural networks in the fields of computer vision, they have been shown to be vulnerable to adversarial examples. An adversarial example is a perturbated image that the magnitude of its difference with its corresponding natural image is small and yet given such example, the network produces incorrect output. In recent years, many approaches have been proposed to increase the robustness of DNNs against adversarial examples with adversarial training being proposed as the most effective defense measure. Approaches based on adversarial training try to increase the robustness of the network by training on the adversarial examples. One of... 

    Parallel Lagrange interpolation on k-ary n-cubes with maximum channel utilization

    , Article Journal of Supercomputing ; Volume 46, Issue 1 , 2008 , Pages 1-14 ; 09208542 (ISSN) Mahabadi, A ; Sarbazi Azad, H ; Khodaie, E ; Navi, K ; Sharif University of Technology
    2008
    Abstract
    This paper proposes an efficient parallel algorithm for computing Lagrange interpolation on k-ary n-cube networks. This is done using the fact that a k-ary n-cube can be decomposed into n link-disjoint Hamiltonian cycles. Using these n link-disjoint cycles, we interpolate Lagrange polynomial using full bandwidth of the employed network. Communication in the main phase of the algorithm is based on an all-to-all broadcast algorithm on the n link-disjoint Hamiltonian cycles exploiting all network channels, and thus, resulting in high-efficiency in using network resources. A performance evaluation of the proposed algorithm reveals an optimum speedup for a typical range of system parameters used... 

    Multifunctional hyperelastic structured surface for tunable and switchable transparency

    , Article Applied Sciences (Switzerland) ; Volume 11, Issue 5 , 2021 , Pages 1-11 ; 20763417 (ISSN) Mahabadi, R. K ; Goudarzi, T ; Fleury, R ; Naghdabadi, R ; Sharif University of Technology
    MDPI AG  2021
    Abstract
    We leverage the crucial hyperelastic properties of a multifunctional structured surface to optimize the reconfigurability of the electromagnetic transmission under large nonlinear mechanical deformations. This multiphysics, multifunctional, hyperelastic structured surface (HSS) offers two simultaneous intriguing functionalities; tunability and switchability. It is made of copper reso-nators and a Polydimethylsiloxane (PDMS) substrate, which is one of the most favorable deformable substrates due to its hyperelastic behavior. The proposed HSS is fabricated via an original cost-effective technique and the multiphysics functionalities are captured in both experimental tests and numerical... 

    A combinational adaptive noise canceller using filter bank

    , Article 6th International Symposium on Image and Signal Processing and Analysis, ISPA 2009, Salzburg, 16 September 2009 through 18 September 2009 ; 2009 , Pages 71-74 ; 9789531841351 (ISBN) Ameri Mahabadi, A ; Hejazi, A ; Akhaee, M. A ; Eshghi, M ; Sharif University of Technology
    2009
    Abstract
    This paper proposes a novel combinational Adaptive Noise Canceller (ANC), which is suitable for non stationary noise environments. Pre-filter bank structure improves the convergence rate leading to less error in real-time applications. During our investigations, we have found out adaptive algorithms have better performance for low frequency subbands. Thus, by using Singular Value Decomposition (SVD) in each subband, a simplified version of variable step-size algorithms has been employed in low frequency subbands; while for high frequency subbands, some conventional techniques have been used. Simulation results show that combination of adaptive and conventional methods have better performance... 

    Optimal Design of Partial State-Feedback Controllers

    , M.Sc. Thesis Sharif University of Technology Farrokhi, Farhad (Author) ; Karimi, Houshang (Supervisor) ; Karimi, Masoud (Supervisor)
    Abstract
    Design of optimal controllers for nonlinear systems and even for linear systems is one of the most important parts of the control science. In optimal controller design, our aim is to maximize or minimize some kind of cost function associated with that particular problem. Such cost functions are usually combining the overall control effort, system’s energy, or some other important specifications of the system. Explicit solution for linear quadratic controllers exists under some mild conditions such as stabilizability of the system. The solution is in the form of a full state-feedback law. But in practical problems, we may not have access to all of the system state variables. The problem can... 

    An Investigation into the Hot Tensile Properties of a Heat Resistant Steel

    , M.Sc. Thesis Sharif University of Technology Mohammad Karimi, Sanaz (Author) ; Karimi Taheri, Ali (Supervisor)
    Abstract
    The microstructures of stainless steels consist of an austenitic matrix with almost continuous network of primery carbides.This class of steel had replaced the traditional super alloys with a reduction in costs and has similar properties under conditions of creep, which is one of the principal degradation mechanisms leading to failure in service at elevated temperaturs , therefore, their mechanical properties such as tensile strength and creep resistance are particularly important in hot deformation. Recently the effects of temperature and aging time on static strain aging in worked stainless steel have been investigated. In this study the deformation behavior of HP-series austenitic... 

    Decentralized adaptive control of large-scale affine and nonaffine nonlinear systems

    , Article IEEE Transactions on Instrumentation and Measurement ; Volume 58, Issue 8 , 2009 , Pages 2459-2467 ; 00189456 (ISSN) Karimi, B ; Menhaj, M. B ; Karimi Ghartemani, M ; Saboori, I ; Sharif University of Technology
    2009
    Abstract
    This paper presents a decentralized adaptive control design for a class of large-scale nonlinear systems with unknown subsystems. When the subsystems are modeled by affine equations, a direct adaptive controller is devised based on the Lyapunov theory, so that the stability of the closed-loop system is guaranteed by introducing a suitably driven adaptive rule. A neuro-based structure is proposed when the subsystems are nonaffine, and the stability analysis is also performed based on the Lyapunov theory. Moreover, the unknown interactions among the subsystems are considered as having a nonlinear function against the simple form considered for the affine case. The proposed controllers are... 

    Decentralized Control of a Multi-DG Microgrid in Islanded Mode of Operation

    , M.Sc. Thesis Sharif University of Technology Moradi Kali Kand, Ramin (Author) ; Karimi, Houshang (Supervisor) ; Karimi, Masoud (Supervisor)
    Abstract
    A control strategy for islanded (autonomous) operation of a microgrid consisting of two Distributed Generation (DG) units is proposed in this thesis. The DG units are connected together in a radial configuration. Each DG unit utilizes a voltage-sourced converter (VSC) to interface to its dedicated load. The DG units and the loads are to operate in the islanded mode of operation. To provide autonomous operation for the microgrid, voltage and frequency of the loads should be regulated. The proposed control strategy utilizes (i) an internal oscillator for frequency control in an open loop manner and (ii) a decentralized servomechanism controller to regulate the load voltage. The microgrid is... 

    Nonlinear adaptive control of grid-connected three-phase inverters for renewable energy applications

    , Article International Journal of Control ; 2015 ; 00207179 (ISSN) Mahdian Dehkordi, N ; Namvar, M ; Karimi, H ; Piya, P ; Karimi Ghartemani, M ; Sharif University of Technology
    2015
    Abstract
    Distributed generation (DG) units are often interfaced to the main grid using power electronic converters including voltage-source converters (VSCs). A VSC offers dc/ac power conversion, high controllability, and fast dynamic response. Because of nonlinearities, uncertainties, and system parameters’ changes involved in the nature of a grid-connected renewable DG system, conventional linear control methods cannot completely and efficiently address all control objectives. In this paper, a nonlinear adaptive control scheme based on adaptive backstepping strategy is presented to control the operation of a grid-connected renewable DG unit. As compared to the popular vector control technique, the... 

    Nonlinear adaptive control of grid-connected three-phase inverters for renewable energy applications

    , Article International Journal of Control ; Volume 90, Issue 1 , 2017 , Pages 53-67 ; 00207179 (ISSN) Mahdian Dehkordi, N ; Namvar, M ; Karimi, H ; Piya, P ; Karimi Ghartemani, M ; Sharif University of Technology
    2017
    Abstract
    Distributed generation (DG) units are often interfaced to the main grid using power electronic converters including voltage-source converters (VSCs). A VSC offers dc/ac power conversion, high controllability, and fast dynamic response. Because of nonlinearities, uncertainties, and system parameters’ changes involved in the nature of a grid-connected renewable DG system, conventional linear control methods cannot completely and efficiently address all control objectives. In this paper, a nonlinear adaptive control scheme based on adaptive backstepping strategy is presented to control the operation of a grid-connected renewable DG unit. As compared to the popular vector control technique, the... 

    Adolf Grünbaum on the steady-state theory and Creatio continua of matter out of nothing

    , Article Zygon ; Volume 46, Issue 4 , 2011 , Pages 857-871 ; 05912385 (ISSN) Karimi, M. M ; Sharif University of Technology
    2011
    Abstract
    The ideas of creatio ex nihilo of the universe and creatio continua of new matter out of nothing entered the arena of natural science with the advent of the Big Bang and the steady-state theories in the mid-twentieth century. Adolf Grünbaum has tried to interpret the steady-state theory in such a way, to show that the continuous formation of new matter out of nothing in this theory can be explained purely physically. In this paper, however, it will be shown that Grünbaum's interpretation encounters at least three problems: not distinguishing between material and efficient causes, inconsistency, and misconceiving the law of density conservation  

    A distortion-free phase-locked loop system for FACTS and power electronic controllers

    , Article Electric Power Systems Research ; Volume 77, Issue 8 , 2007 , Pages 1095-1100 ; 03787796 (ISSN) Karimi Ghartemani, M ; Sharif University of Technology
    2007
    Abstract
    This paper presents a single-phase phase-locked loop (PLL) system which is primarily free from the double-frequency ripples from which the conventional PLL system suffers. The proposed PLL is then extended to reject the harmonic components from the input signal and to estimate the phase-angle and frequency of the distorted input signal with no error. Three units of the proposed PLL can be used in three-phase power systems, such as FACTS and HVDC converters, to estimate the phase-angles of the individual phases with no double-frequency ripples and without sensitivity to the presence of harmonics and inter-harmonics. This makes the proposed PLL unique and desirable for applications which... 

    A novel three-phase magnitude-phase-locked loop system

    , Article IEEE Transactions on Circuits and Systems I: Regular Papers ; Volume 53, Issue 8 , 2006 , Pages 1792-1802 ; 10577122 (ISSN) Karimi Ghartemani, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2006
    Abstract
    A novel three-phase magnitude-phase-locked-loop system (3MPLL) for use in the general area of three-phase (power, energy and power electronic) systems is introduced. The proposed 3MPLL suppresses the noise and distortion from the input signal, mitigates the unbalance, and synthesizes the instantaneous positive-sequence component of the input signal; thus it operates as a nonlinear adaptive notch (or band-pass) filter. The 3MPLL also adaptively tracks and estimates the magnitude, phase angle, and frequency of the input signal; thus, its operation as a nonlinear state estimator. Characteristics of the 3MPLL including its mathematical equations as well as steady-state and dynamic responses are... 

    A Study of Iran Gas Export Markets and Strategic Proposal for Entering

    , M.Sc. Thesis Sharif University of Technology Karimi, Maryam (Author) ; Kermanshah, Ali (Supervisor)
    Abstract
    Possessing second place among gas reserve owner countries worldwide, Iran enjoys a very particular position in energy supply field. The crude oil is about to be replaced by natural gas in fuel sector because of growing demand for natural gas along with depletion of crude oil reserves. Some other drivers to this change are the increase in the known reserves of natural gas, the need to monetize stranded gas reserves and the environmental pressure to minimize the flaring of associated gas and carbon dioxide emissions. In such conditions the optimum consumption of these national abundant resources results in obtaining considerable revenues and strong presence of Iran in world consumption... 

    A Method for Querying on Encrypted XML Data

    , M.Sc. Thesis Sharif University of Technology Karimi, Maryam (Author) ; Jalili, Rasool (Supervisor)
    Abstract
    When organizations prefer to outsource their data, security protection of data will be more important. Using cryptography in addition to access control techniques is a natural way for saving confidentiality of data against untrusted server. However, encryption and decryption of data result in database performance degradation. In such a situation all the information stored in encrypted form, one cannot make the selection on the database content any more. Data should be decrypted first, so an unwilling tradeoff between the security and performance is normally forced. The appropriate approaches to increase the performance are methods to deal directly with the encrypted data without firstly...