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On nodal domains and higher-order Cheeger inequalities of finite reversible Markov processes [electronic resource]
, Article Stochastic Processes and their Applications ; Volume 122, Issue 4, April 2012, Pages 1748–1776 ; Javadi, Ramin ; Miclo, Laurent ; Sharif Univercity of Technology
Abstract
Let LL be a reversible Markovian generator on a finite set View the MathML sourceV. Relations between the spectral decomposition of LL and subpartitions of the state space View the MathML sourceV into a given number of components which are optimal with respect to min–max or max–min Dirichlet connectivity criteria are investigated. Links are made with higher-order Cheeger inequalities and with a generic characterization of subpartitions given by the nodal domains of an eigenfunction. These considerations are applied to generators whose positive rates are supported by the edges of a discrete cycle ZNZN, to obtain a full description of their spectra and of the shapes of their eigenfunctions, as...
Robust regulation and tracking system design for multivariable control of the tape transport mechanism
, Article Microsystem Technologies ; Vol. 18, Issue. 5 , 2012 , pp. 557-573 ; ISSN: 09467076 ; Bakhtiari-Nejad, F ; Alasty, A ; Sharif University of Technology
Abstract
Tape mechanisms must be able to transport the tape with a constant velocity for achieving high rate of data transfer. In this paper, a multivariable model of tape transport mechanism including the take-up and supply reel servos for tape tension control and capstan servo for speed control is considered. To achieve desired performance,pole-placement approach based on general canonical control form (GCCF) is used. Instead of using expensive tension sensors, an observer is designed. A regulator system is developed for disturbance rejection; and a modified integral control is designed for perfect tracking of desired setpoints in tape speed and tensions. Since the real dynamic model associates...
Performance control of a tape transport mechanism using entire eigenstructure assignment
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings ; Vol. 10, Issue PART A , 2010 , pp. 133-140 ; ISBN: 9780791843833 ; Hajikolaei, K. H ; Motamedi, M ; Alasty, A ; Sharif University of Technology
Abstract
To achieve high rate of data transfer, tape mechanisms must be able to transport the tape with a constant velocity for scanning. During this process, it is desired to make the rise time minimized without timing and data transfer errors. In this paper, three servo systems including the take-up and supply reel servos for tape tension control and capstan servo for speed control are considered. So, tape transport mechanisms can be described with a nonlinear multi-input multi-output system (MIMO). After state-space representation of the problem, feedback control is designed for tracking objective. It should be mentioned that an increase in the speed of time response of system corresponds to an...
Connectedness of users-items networks and recommender systems
, Article Applied Mathematics and Computation ; Vol. 243 , 2014 , Pages 578-584 ; ISSN: 00963003 ; 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...
Optimal ground state energy of two-phase conductors
, Article Electronic Journal of Differential Equations ; Vol. 2014 , 2014 ; ISSN: 10726691 ; Yousefnezhad, M ; Sharif University of Technology
Abstract
We consider the problem of distributing two conducting materials in a ball with xed proportion in order to minimize the rst eigenvalue of a Dirichlet operator. It was conjectured that the optimal distribution consists of putting the material with the highest conductivity in a ball around the center. In this paper, we show that the conjecture is false for all dimensions greater than or equal to two
The effects of nonlinearities on the vibration of viscoelastic sandwich plates
, Article International Journal of Non-Linear Mechanics ; Vol. 62 , 2014 , Pages 41-57 ; ISSN: 00207462 ; Haddadpour, H ; Navazi, H. M ; Sharif University of Technology
Abstract
The nonlinear free and forced bending vibration of sandwich plates with incompressible viscoelastic core is investigated under the effects of different source of nonlinearities. For the core constrained between stiffer layers, the transverse shear strains, as well as the rotations are assumed to be moderate. The linear and quadratic displacement fields are also adopted for the in-plane and out-of-plane displacements of the core, respectively. The assumption of moderate transverse strains requires a nonlinear constitutive equation which is obtained from a single-integral nonlinear viscoelastic model using the assumed order of magnitudes for linear strains and rotations. The 5th-order method...
The multiplicity of Laplacian eigenvalue two in unicyclic graphs
, Article Linear Algebra and Its Applications ; Vol. 445 , 2014 , pp. 18-28 ; Kiani, D ; Mirzakhah, M ; Sharif University of Technology
Abstract
Let G be a graph and L(G) be the Laplacian matrix of G. In this paper, we explicitly determine the multiplicity of Laplacian eigenvalue 2 for any unicyclic graph containing a perfect matching
Axial-torsional vibrations of rotating pretwisted thin walled composite beams
, Article International Journal of Mechanical Sciences ; Vol. 80 , 2014 , pp. 93-101 ; ISSN: 00207403 ; Haddadpour, H ; Sharif University of Technology
Abstract
Axial-torsional vibrations of rotating pretwisted thin-walled composite box beams exhibiting primary and secondary warping are investigated. Considering the nonlinear strain-displacement relations, the coupled nonlinear axial-torsional equations of motion are derived using Hamilton's principle. Ignoring the axial inertia term leads to differential equation of motion in terms of elastic torsion in the case of axially immovable beams. Centrifugal load in the presence of material anisotropy and pretwist angle leads to an induced static torque. The nonlinear equation should be linearized about the corresponding equilibrium state to obtain the linear differential equation of motion. Extended...
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 ; 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 ; 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...
Collective dynamics of interacting particles in unsteady flows
, Article SIAM Journal on Applied Dynamical Systems ; Vol. 13, Issue. 1 , 2014 , pp. 194-209 ; ISSN: 15360040 ; Jalali, M. A ; Sharif University of Technology
Abstract
We use the Fokker-Planck equation and its moment equations to study the collective behavior of interacting particles in unsteady one-dimensional flows. Particles interact according to a longrange attractive and a short-range repulsive potential field known as Morse potential. We assume Stokesian drag force between particles and their carrier fluid and find analytic single-peaked traveling solutions for the spatial density of particles in the catastrophic phase. In steady flow conditions the streaming velocity of particles is identical to their carrier fluid, but we show that particle streaming is asynchronous with an unsteady carrier fluid. Using linear perturbation analysis, the stability...
Re-interpreting simultaneous buckling modes of axially compressed isotropic conical shells
, Article Thin-Walled Structures ; Vol. 84 , November , 2014 , pp. 360-368 ; ISSN: 02638231 ; 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...
Thickness optimization of polyurethane floor insulation based on analysis of the heat transfer in a multi-layer
, Article ASME 2014 12th Biennial Conference on Engineering Systems Design and Analysis, ESDA 2014 ; Vol. 3, issue , 2014 ; Saidi, M. H ; Reshadi, M ; Sharif University of Technology
Abstract
During the year, due to weather conditions, the temperature fluctuations at surface level cause problems in underground pipes as a result of freezing water. One of the best prevention strategies is the use of polyurethane floor insulation for keeping the temperature of clay above zero degrees Celsius. In this study to calculate the minimum thickness of polyurethane insulation layer, the differential equation of energy is solved based on principle of separation of variables using imaginary eigenvalues for consistency with the temperature distribution in multi-layer consist of asphalt, gravel and polyurethane with finite thickness and clay as a semiinfinite medium with periodic thermal...
The electro-elastic scattered fields of an SH-wave by an eccentric two-phase circular piezoelectric sensor in an unbounded piezoelectric medium
, Article Mechanics of Materials ; Vol. 75 , 2014 , pp. 1-12 ; ISSN: 01676636 ; Jarfi, H ; Rashidinejad, E ; Sharif University of Technology
Abstract
The dynamic equivalent inclusion method (DEIM) which was first proposed by Fu and Mura (1983), in its original context has some shortcomings, which were pointed out and remedied by Shodja and Delfani (2009) who introduced the new consistency conditions along with the related micromechanically substantiated notion of eigenstress and eigenbody-force fields. However, these theories are bound to elastic media with isotropic phases. The present work extends the idea of the above-mentioned new DEIM to the dynamic electro-mechanical equivalent inclusion method (DEMEIM) for the treatment of the scattering of SH-waves by a two-phase circular piezoelectric obstacle bonded to a third phase...
Free vibration analysis of Mindlin plates partially resting on Pasternak foundation
, Article International Journal of Mechanical Sciences ; Volume 75 , 2013 , Pages 1-7 ; 00207403 (ISSN) ; Aghdam, M. M ; Fallah, A ; Sharif University of Technology
Abstract
In this paper, the generalized differential quadrature (GDQ) method is used to study free vibration of moderately thick rectangular plate partially resting on Pasternak foundation. The foundation is considered to support the plate either completely or partially. The governing equations which consist of a system of partial differential equations (PDEs) are obtained based on the first-order shear deformation theory. Various combinations of simply supported, clamped and free boundary conditions are considered. Application of the GDQ method to the governing PDEs resulted in a system of algebraic equations. Solution of this system with accordance to the considered boundary conditions leads to an...
Assessment of three preconditioning schemes for solution of the two-dimensional Euler equations at low Mach number flows
, Article International Journal for Numerical Methods in Engineering ; Volume 89, Issue 1 , 2012 , Pages 20-52 ; 00295981 (ISSN) ; Kamali Moghadam, R ; Sharif University of Technology
Abstract
Three preconditioners proposed by Eriksson, Choi and Merkel, and Turkel are implemented in a 2D upwind Euler flow solver on unstructured meshes. The mathematical formulations of these preconditioning schemes for different sets of primitive variables are drawn, and their eigenvalues and eigenvectors are compared with each other. For this purpose, these preconditioning schemes are expressed in a unified formulation. A cell-centered finite volume Roe's method is used for the discretization of the preconditioned Euler equations. The accuracy and performance of these preconditioning schemes are examined by computing steady low Mach number flows over a NACA0012 airfoil and a two-element...
Free vibration analysis of FGM beams with different boundary conditions using RKPM meshless method
, Article Proceedings of the ASME Design Engineering Technical Conference, 28 August 2011 through 31 August 2011 ; Volume 1, Issue PARTS A AND B , August , 2011 , Pages 1187-1191 ; 9780791854785 (ISBN) ; Ahmadian, M. T ; Sharif University of Technology
Abstract
This paper presents free vibration analysis of functionally graded material (FGM) beams with different boundary conditions, using RKPM (Reproducing Kernel Particle Method), which is a meshless method. System of equations of motion is derived by using Lagrange's method under the assumption of Euler-Bernoulli beam theory. Boundary conditions of beam are taken into account by using Lagrange multipliers. It is assumed that material properties of the beam vary continuously in the thickness direction according to the power-law form. RKPM is applied to obtain eigenvalue equation of vibration and natural frequencies are obtained. It should be noted that for special cases where the beam is uniform,...
Active control of robotic manipulators vibration via feedback control
, Article 17th International Congress on Sound and Vibration 2010, ICSV 2010, 18 July 2010 through 22 July 2010 ; Volume 1 , 2010 , Pages 464-471 ; 9781617822551 (ISBN) ; Bakhtiari Nejad, F ; Sadighi, M ; Alasty, A ; Sharif University of Technology
Abstract
In this paper, a robotic manipulator modelled as a cantilever rotating Euler-Bernoulli beam is considered. Control objective is achieving a desired angular rotation of the manipulator tip while its lateral vibration is suppressed. An external driving torque is the control input of the system. Two dynamic transfer functions are derived to describe beam tip motion and angular rotation in terms of the desired angular rotation. After state-space representation of the problem, an observer is designed to estimate state variables of the system. Then, a feedback control is designed for both regulation and tracking objectives. Eigenvalues are chosen such that an appropriate response is achieved while...
Development of a 2-D 2-group neutron noise simulator for hexagonal geometries
, Article Annals of Nuclear Energy ; Volume 37, Issue 8 , 2010 , Pages 1089-1100 ; 03064549 (ISSN) ; Vosoughi, N ; Zahedinejad, E ; Sharif University of Technology
Abstract
In this paper, the development of a neutron noise simulator for hexagonal-structured reactor cores using both the forward and the adjoint methods is reported. The spatial discretisation of both 2-D 2-group static and dynamic equations is based on a developed box-scheme finite difference method for hexagonal mesh boxes. Using the power iteration method for the static calculations, the 2-group neutron flux and its adjoint with the corresponding eigenvalues are obtained by the developed static simulator. The results are then benchmarked against the well-known CITATION computer code. The dynamic calculations are performed in the frequency domain which leads to discarding of the time...
Performance control of a tape transport mechanism using entire eigenstructure assignment
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009 ; Volume 10, Issue PART A , 2010 , Pages 133-140 ; 9780791843833 (ISBN) ; Haji Hajikolaei, K ; Motamedi, M ; Alasty, A ; Sharif University of Technology
Abstract
To achieve high rate of data transfer, tape mechanisms must be able to transport the tape with a constant velocity for scanning. During this process, it is desired to make the rise time minimized without timing and data transfer errors. In this paper, three servo systems including the take-up and supply reel servos for tape tension control and capstan servo for speed control are considered. So, tape transport mechanisms can be described with a nonlinear multi-input multi-output system (MIMO). After state-space representation of the problem, feedback control is designed for tracking objective. It should be mentioned that an increase in the speed of time response of system corresponds to an...