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    Sensitivity-based generators redispatch to improve electromechanical mode damping considering transmission lines resistance

    , Article 27th Iranian Conference on Electrical Engineering, ICEE 2019, 30 April 2019 through 2 May 2019 ; 2019 , Pages 491-496 ; 9781728115085 (ISBN) Setareh, M ; Parniani, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    This paper proposes a novel formula to calculate sensitivities of electromechanical modes to generators active power changes. Quadratic eigenvalue problem is applied to construct the framework of the proposed formula. Sensitivity factors are calculated using power system model parameters and power flow variables, which can be either obtained via state estimation or measured directly by phasor measurement units. The 39-bus New England power system is used to verify performance of the proposed method  

    Connectedness of users-items networks and recommender systems

    , Article Applied Mathematics and Computation ; Vol. 243 , 2014 , Pages 578-584 ; ISSN: 00963003 Gharibshah, J ; Jalili, M ; Sharif University of Technology
    Abstract
    Recommender systems have become an important issue in network science. Collaborative filtering and its variants are the most widely used approaches for building recommender systems, which have received great attention in both academia and industry. In this paper, we studied the relationship between recommender systems and connectivity of users-items bipartite network. This results in a novel recommendation algorithm. In our method recommended items are selected based on the eigenvector corresponding to the algebraic connectivity of the graph - the second smallest eigenvalue of the Laplacian matrix. Since recommending an item to a user equals to adding a new link to the users-items bipartite... 

    MIMO radar beamforming using orthogonal decomposition of correlation matrix

    , Article Circuits, Systems, and Signal Processing ; Volume 32, Issue 4 , 2013 , Pages 1791-1809 ; 0278081X (ISSN) Shadi, K ; Behnia, F ; Sharif University of Technology
    2013
    Abstract
    MIMO radar is the next generation radar which transmits arbitrary waveforms at each one of its apertures. It has been shown that the design of waveforms for MIMO radars in order to synthesize a desired spatial beampattern is mapped into a waveform correlation matrix R design in the narrowband case. As of now, given a desired beampattern or estimated locations information of targets, calculating R has been modeled as an optimization problem like semi-definite programming. Also, in some special cases like rectangular beampattern, closed-form solutions for R has been proposed. In this paper, we introduce a fast algorithm which is capable of designing R in order to achieve more arbitrary... 

    Spectral distribution of the exponentially windowed sample covariance matrix

    , Article ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, 25 March 2012 through 30 March 2012, Kyoto ; 2012 , Pages 3529-3532 ; 15206149 (ISSN) ; 9781467300469 (ISBN) Yazdian, E ; Bastani, M. H ; Gazor, S ; Sharif University of Technology
    IEEE  2012
    Abstract
    In this paper, we investigate the effect of applying an exponential window on the limiting spectral distribution (l.s.d.) of the exponentially windowed sample covariance matrix (SCM) of complex array data. We use recent advances in random matrix theory which describe the distribution of eigenvalues of the doubly correlated Wishart matrices. We derive an explicit expression for the l.s.d. of the noise-only data. Simulations are performed to support our theoretical claims  

    A lower bound for algebraic connectivity based on the connection-graph- stability method

    , Article Linear Algebra and Its Applications ; Volume 435, Issue 1 , Sep , 2011 , Pages 186-192 ; 00243795 (ISSN) Ajdari Rad, A ; Jalili, M ; Hasler, M ; Sharif University of Technology
    2011
    Abstract
    This paper introduces the connection-graph-stability method and uses it to establish a new lower bound on the algebraic connectivity of graphs (the second smallest eigenvalue of the Laplacian matrix of the graph) that is sharper than the previously published bounds. The connection-graph-stability score for each edge is defined as the sum of the lengths of the shortest paths making use of that edge. We prove that the algebraic connectivity of the graph is bounded below by the size of the graph divided by the maximum connection-graph-stability score assigned to the edges  

    Computing all the Floquet eigenfunctions of oscillators using harmonic balance Jacobian matrices

    , Article IET Circuits, Devices and Systems ; Volume 5, Issue 4 , July , 2011 , Pages 257-266 ; 1751858X (ISSN) Jahanbakht, S ; Farzaneh, F ; Sharif University of Technology
    2011
    Abstract
    Floquet eigenfunctions and Floquet exponents are encountered in stability and noise analysis of circuits operating at large signal periodic regime. It is analytically verified that the spectrum vectors of the left-hand and right-hand Floquet eigenfunctions and the Floquet exponents (Floquet eigenpairs) are members of the harmonic balance eigenvalues and eigenvectors (HB eigenpairs). The relationships between other HB eigenpairs with the Floquet eigenpairs are discussed. This discussion leads to a practical algorithm for computing the Floquet eigenpairs through HB eigenpairs. Furthermore, it is analytically verified that the main arguments of the study are consistent with the... 

    Fast estimation of propagation constants in lamellar gratings needless of solving the eigenvalue equation

    , Article 27th Iranian Conference on Electrical Engineering, ICEE 2019, 30 April 2019 through 2 May 2019 ; 2019 , Pages 1342-1346 ; 9781728115085 (ISBN) Faghihifar, E ; Akbari, M ; Hossein Nekuee, S. A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    Fourier-based modal methods are among the most significant tools for accurate numerical analysis of grating structures. However, they mostly lead to time consuming and memory hungry eigenvalue problems, particularly when large dielectric constants or high contrasts are involved. We have found an asymptotic semi-empirical relationship for the propagation constants of a lamellar grating, obtained from Fourier-based modal methods. Hence, given any truncation order, it is possible to estimate propagation constants without having to solve the eigenvalue equation. We observed propagation constants only depend on permittivities, filling factors, and the unit cell size, while the dependence on the... 

    Extraction of effective constitutive parameters of artificial media using Bloch modes

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 36, Issue 11 , 2019 , Pages 3226-3235 ; 07403224 (ISSN) Sheikh Ansari, A ; Rejaei, B ; Sharif University of Technology
    OSA - The Optical Society  2019
    Abstract
    The effective constitutive parameters of a three-dimensional periodic structure are calculated using its Bloch modes. These modes and their propagation constants are obtained from eigenvectors and eigenvalues of the generalized transfer matrix of a unit layer of the structure. Effective bulk permittivity and permeability tensors of the medium are obtained when two of the Bloch modes are dominant, i.e., propagate without significant decay inside the medium. The effect of the strongly decaying Bloch modes, which are excited at the interface with a conventional medium, are included by means of surface impedance matrices. The results are in excellent agreement with full-wave electromagnetic... 

    Extraction of effective constitutive parameters of artificial media using bloch modes

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 36, Issue 11 , 2019 , Pages 3226-3235 ; 07403224 (ISSN) Sheikh Ansari, A ; Rejaei, B ; Sharif University of Technology
    OSA - The Optical Society  2019
    Abstract
    The effective constitutive parameters of a three-dimensional periodic structure are calculated using its Bloch modes. These modes and their propagation constants are obtained from eigenvectors and eigenvalues of the generalized transfer matrix of a unit layer of the structure. Effective bulk permittivity and permeability tensors of the medium are obtained when two of the Bloch modes are dominant, i.e., propagate without significant decay inside the medium. The effect of the strongly decaying Bloch modes, which are excited at the interface with a conventional medium, are included by means of surface impedance matrices. The results are in excellent agreement with full-wave electromagnetic... 

    The main eigenvalues of signed graphs

    , Article Linear Algebra and Its Applications ; 2020 Akbari, S ; França, F. A. M ; Ghasemian, E ; Javarsineh, M ; de Lima, L. S ; Sharif University of Technology
    Elsevier Inc  2020
    Abstract
    A signed graph Gσ is an ordered pair (V(G),E(G)), where V(G) and E(G) are the set of vertices and edges of G, respectively, along with a map σ that signs every edge of G with +1 or −1. An eigenvalue of the associated adjacency matrix of Gσ, denoted by A(Gσ), is a main eigenvalue if the corresponding eigenspace has a non-orthogonal eigenvector to the all-one vector j. We conjectured that for every graph G≠K2,K4{e}, there is a switching σ such that all eigenvalues of Gσ are main. We show that this conjecture holds for every Cayley graphs, distance-regular graphs, vertex and edge-transitive graphs as well as double stars and paths. © 2020 Elsevier Inc  

    Fast estimation of propagation constants in crossed gratings

    , Article Journal of Optics (United Kingdom) ; Volume 22, Issue 2 , 2020 Faghihifar, E ; Akbari, M ; Nekuee, S. A. H ; Sharif University of Technology
    IOP Publishing Ltd  2020
    Abstract
    Fourier-based modal methods are among the most effective numerical tools for the accurate analysis of crossed gratings. However, leading to computationally expensive eigenvalue equations significantly restricts their applicability, particularly when large truncation orders are required. The resultant eigenvalues are the longitudinal propagation constants of the grating and play a key role in applying the boundary conditions, as well as in the convergence and stability analyses. This paper aims to propose simple techniques for the fast estimation of propagation constants in crossed gratings, predominantly with no need to solve an eigenvalue equation. In particular, we show that for regular... 

    Optimal exploitation of the resource in remote state preparation

    , Article Physical Review A ; Volume 102, Issue 1 , 15 July , 2020 Nikaeen, M ; Ramezani, M ; Bahrampour, A ; Sharif University of Technology
    American Physical Society  2020
    Abstract
    Transmission efficiency (TE) of remote state preparation (RSP) with a shared quantum state and one bit of classical communication is considered. Following Dakić et al. [Nat. Phys. 8, 666 (2012)10.1038/nphys2377], the encoding and decoding operators of the protocol are restricted to the physically relevant classes of projective measurements and unitary operators, respectively. It is shown that contrary to the previous arguments, the quadratic fidelity as well as the linear fidelity could be a valid figure of merit to quantify the TE of RSP. Then, the TE of the protocol in terms of both linear and quadratic fidelities is evaluated in a fully optimized scenario which includes the maximization... 

    A methodology for analyzing the transient availability and survivability of a system with repairable components

    , Article Applied Mathematics and Computation ; Volume 184, Issue 2 , 2007 , Pages 300-307 ; 00963003 (ISSN) Amiri, M ; Ghassemi Tari, F ; Sharif University of Technology
    2007
    Abstract
    In this paper we present a method for transient analysis of availability and survivability of a system with the identical components and identical repairmen. The considered system is supposed to consist of series of k-out-of-n or parallel components. We employed the Markov models, eigen vectors and eigenvalues for analyzing the transient availability and survivability of the system. The method is implemented through an algorithm which is tested in MATLAB programming environment. The new method enjoys a stronger mathematical foundation and more flexibility for analyzing the transient availability and survivability of the system. © 2006 Elsevier Inc. All rights reserved  

    Intrinsic expressions for arbitrary stress tensors conjugate to general strain tensors

    , Article Scientia Iranica ; Volume 14, Issue 5 , 2007 , Pages 486-493 ; 10263098 (ISSN) Sohrabpour, S ; Naghdabadi, R ; Asghari, M ; Sharif University of Technology
    Sharif University of Technology  2007
    Abstract
    In this paper, a unified explicit tensorial relation is sought between two stress tensors conjugate to arbitrary and general Hill strains. The approach used for deriving the tensorial relation is based on the eigenprojection method. The result is, indeed, a generalization of the relations that were derived by Farahani and Naghadabadi [1] in 2003 from a component to intrinsic form. The result is unified in the sense that it is valid for all cases of distinct and coalescent principal stretches. Also, in the case of three dimensional Euclidean inner product space, using the derived unified relation, some expressions for the conjugate stress tensors are presented. © Sharif University of... 

    Unified basis-free relation between two stress tensors conjugate to arbitrary Hill's strain measures

    , Article ASME PVP2006/ICPVT-11 Conference, Vancouver, BC, 23 July 2006 through 27 July 2006 ; Volume 2006 , 2006 ; 0277027X (ISSN); 0791837823 (ISBN); 9780791837825 (ISBN) Asghari, M ; Naghdabadi, R ; Sharif University of Technology
    American Society of Mechanical Engineers(ASME)  2006
    Abstract
    The concept of energy conjugacy for stress and strain measures states that a stress tensor T is conjugate to a strain measure E if T: Ė provides the rate of change of the internal energy per unit reference volume of the body in an adiabatic process. The applications of the conjugate stress and strain measures are in the development of the basic relations in nonlinear analysis of solids. In this paper using eigenprojection method, unified explicit basis-free relation between two arbitrary stress tensors T(f) and T (g), respectively conjugate to two measures of Hill's strains is determined. The result is valid for arbitrary dimension of the Euclidean inner product space and for all cases of... 

    Linear analysis of the stability of particle-laden stratified shear layers

    , Article Canadian Journal of Physics ; Vol. 92, issue. 2 , 2014 , pp. 103-115 ; ISSN: 00084204 Khavasi, E ; Firoozabadi, B ; Afshin, H
    Abstract
    Hydrodynamic instabilities at the interface of stratified shear layers could occur in various modes and have an important role in the mixing process. In this work, the linear stability analysis in the temporal framework is used to study the stability characteristics of a particle-laden stratified two-layer flow for two different background density profiles: smooth (hyperbolic tangent) and piecewise linear. The effect of parameters, such as bed slope, viscosity, and particle size, on the stability is also considered. The pseudospectral collocation method employing Chebyshev polynomials is used to solve two coupled eigenvalue equations. Based on the results, there are some differences in the... 

    Inverse vibration problem for un-damped 3-dimensional multi-story shear building models

    , Article Journal of Sound and Vibration ; Volume 333, Issue 1 , 6 January , 2014 , Pages 99-113 ; ISSN: 0022460X Dolatshahi, K. M ; Rofooei, F. R ; Sharif University of Technology
    Abstract
    Various researchers have contributed to the identification of the mass and stiffness matrices of two dimensional (2-D) shear building structural models for a given set of vibratory frequencies. The suggested methods are based on the specific characteristics of the Jacobi matrices, i.e., symmetric, tri-diagonal and semi-positive definite matrices. However, in case of three dimensional (3-D) structural models, those methods are no longer applicable, since their stiffness matrices are not tri-diagonal. In this paper the inverse problem for a special class of vibratory structural systems, i.e., 3-D shear building models, is investigated. A practical algorithm is proposed for solving the inverse... 

    Re-interpreting simultaneous buckling modes of axially compressed isotropic conical shells

    , Article Thin-Walled Structures ; Vol. 84 , November , 2014 , pp. 360-368 ; ISSN: 02638231 Shakouri, M ; Spagnoli, A ; Kouchakzadeh, M. A ; Sharif University of Technology
    Abstract
    Elastic stability of shell structures under certain loading conditions is characterized by a dramatically unstable postbuckling behavior. The presence of simultaneous 'competing' buckling modes (corresponding to the same critical buckling load) is understood to be largely responsible for such behavior. In this paper, within the framework of linear bifurcation eigenvalue analysis and Donnell shallow shell theory, the presence of simultaneous buckling modes in axially compressed isotropic cones is determined using the semi-analytical method of Galerkin. The results are presented in the plane of the dimensionless reciprocal meridional and circumferential buckling half wavelengths, and are... 

    Bending-torsional flutter of a cantilevered pipe conveying fluid with an inclined terminal nozzle

    , Article Journal of Sound and Vibration ; Volume 332, Issue 12 , 2013 , Pages 3002-3014 ; 0022460X (ISSN) Firouz Abadi, R. D ; Askarian, A. R ; Kheiri, M ; Sharif University of Technology
    2013
    Abstract
    Stability analysis of a horizontal cantilevered pipe conveying fluid with an inclined terminal nozzle is considered in this paper. The pipe is modelled as a cantilevered Euler-Bernoulli beam, and the flow-induced inertia, Coriolis and centrifugal forces along the pipe as well as the follower force induced by the jet-flow are taken into account. The governing equations of the coupled bending-torsional vibrations of the pipe are obtained using extended Hamilton's principle and are then discretized via the Galerkin method. The resulting eigenvalue problem is then solved, and several cases are examined to determine the effect of nozzle inclination angle, nozzle aspect ratio, mass ratio and... 

    The impact of wind farms with doubly fed induction generators on power system electromechanical oscillations

    , Article Renewable Energy ; Volume 50 , 2013 , Pages 780-785 ; 09601481 (ISSN) Jafarian, M ; Ranjbar, A. M ; Sharif University of Technology
    2013
    Abstract
    Introduction of large amounts of new wind generation can affect the small signal stability of power systems with three mechanisms: displacing synchronous generators (SGs); reducing SGs power generation; and the dynamics of wind farms (WFs) interacting with the electromechanical mode of SGs. In this paper a novel approach is developed to investigate the impact of the latter mechanism on existing power systems oscillations. In this approach, the dynamic behavior of grid connected WFs is studied independent of the dynamic behavior of system SGs. This approach helps to identify the conditions in which the dynamics of WFs may interact with the electromechanical mode of SGs. Also it helps to...