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eigenvalues-and-eigenfunctions
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Total 205 records
Response of a suspended cable to narrow-band random excitation with peaked P.S.D
, Article Mathematical and Computer Modelling ; Volume 41, Issue 11-12 , 2005 , Pages 1203-1212 ; 08957177 (ISSN) ; Mehri, B ; Younesian, D ; Sharif University of Technology
2005
Abstract
The response of a suspended cables subjected to narrow-band random excitations with two types of peaked P.S.D. is formulated and analyzed. Banach fixed-point theorem is used for eigenfunction analysis of the differential-integral equations of motion for the first time in this paper. Fredholm approach also is used in the free vibration analysis of the suspended cable and then using Galerkin mode approximation method, power spectral density, and root mean square of the response are computed for two practical types of excitation. All of the calculated results converted to dimensionless quantities make their usage easier in vibration analysis of some practical cases such as vibration of moving...
On the existence of periodic solutions for certain differential equations
, Article Journal of Computational and Applied Mathematics ; Volume 174, Issue 2 , 2005 , Pages 239-249 ; 03770427 (ISSN) ; Niksirat, M. A ; Sharif University of Technology
2005
Abstract
Here we are concerned with the problem of the existence of periodic solution for certain second and third-order nonlinear differential equations. Our method here is to consider the problem as an eigenvalue problem and treat it by the topological degree theory. In particular we establish the conditions of the existence of periodic solution first for a simpler system which is homotopic to the original system and then generalize the obtained results for the focal system. The method employed here is applicable also for a system of nonlinear differential equations just with simple modifications. Finally, we present some specific examples numerically to show that the results are valid and...
Overall behavior of composites with periodic multi-inhomogeneities
, Article Mechanics of Materials ; Volume 37, Issue 2-3 SPEC. ISS , 2005 , Pages 343-353 ; 01676636 (ISSN) ; Roumi, F ; Sharif University of Technology
2005
Abstract
When applying the equivalent inclusion method (EIM) to a composite material with non-dilute distribution of reinforcement particles, due to the complex interaction between the particles, the homogenizing eigenstrain field will in general be highly nonlinear. The interaction becomes more complex, when the reinforcements are multi-phase particles, i.e., the core inhomogeneity is surrounded by many layers of coatings. In this paper, a treatment for an accurate determination of the distribution of homogenizing eigenstrain fields corresponding to composites with non-dilute periodic distribution of multi-phase reinforcement particles is given. The proposed method is applicable to problems, where...
A new reduced-order modeling approach based on fluid eigenmodes and boundary element method
, Article 23rd AIAA Applied Aerodynamics Conference, Toronto, ON, 6 June 2005 through 9 June 2005 ; Volume 2 , 2005 , Pages 1245-1252 ; 10485953 (ISSN) ; Nobari, A. S ; Shahverdi, H ; Haddadpour, H ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2005
Abstract
This paper presents a new reduced-order modeling approach based on boundary element method. In this approach the eigenvalue problem of the unsteady flows is defined based on the unknown wake singularities. By constructing this reduced-order model, the body quasi-static eigenmodes are removed from the eigensystem and it is possible to obtain satisfactory results without static correction technique when enough eigenmodes are used. In addition to the conventional method, Eigenanalysis and reduced-order modeling of unsteady flows over a NACA 0012 airfoil and a wing with NACA 0012 section are performed using this new ROM method. Numerical examples are presented that demonstrate the accuracy and...
Reduced-order modeling of unsteady flows without static correction requirement
, Article Journal of Aircraft ; Volume 42, Issue 4 , 2005 , Pages 882-886 ; 00218669 (ISSN) ; Haddadpour, H ; Esfahanian, V ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2005
Abstract
A new reduced-order modeling approach is presented. This approach is based on fluid eigenmodes and without using the static correction. The vortex lattice method is used to analyze unsteady flows over two-dimensional airfoils and three-dimensional wings. Eigenanalysis and reduced-order modeling are performed using a conventional method with and without the static correction technique. In addition to the conventional method, eigenanalysis and reduced-order modeling are also performed using the new proposed method, that is, without static correction requirement. Numerical examples are presented to demonstrate the accuracy and computational efficiency of the proposed method. Based on the...
Characterization of two-qubit perfect entanglers
, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 70, Issue 5 A , 2004 , Pages 052313-1-052313-9 ; 10502947 (ISSN) ; Sharif University of Technology
2004
Abstract
The problem of the characterization of perfect entanglers was investigated. Perfect entanglers have been defined as unitary operators that can generate maximally entangled states from some suitably chosen separable states. Some well defined tools have also been used to measure the entangling properties of quantum operators and two-qubit states. It was found that such tools help to analyze perfect entanglers and also have the unique property of maximally entangling a complete set of orthonormal product vectors. The results show that the qubit gates provided minimum universal gate construction and two of them were necessary and sufficient in implementation of a generic two-qubit gate
Thermal entanglement of spins in the Heisenberg model at low temperatures
, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 70, Issue 5 A , 2004 , Pages 052307-1-052307-5 ; 10502947 (ISSN) ; Karimipour, V ; Sharif University of Technology
2004
Abstract
The entanglement between two spins in the ferromagnetic Heisenberg chain at low temperatures was calculated. It was shown that if a magnetic field is applied to a ferromagnetic Heisenberg chain, then pairwise entanglement develops between spins at arbitrary given states. It was also shown that the entanglement profile is a Gaussian with a characteristic length depending on the temperature and the coupling between spins only when the ground state and the one-particle states are populated. The magnetic field was shown to affect only the amplitude of the profile and not its characteristic length
Oscillator strength calculations in color centers of diamond and the role of spin
, Article European Physical Journal B ; Volume 39, Issue 4 , 2004 , Pages 441-446 ; 14346028 (ISSN) ; Vesaghi, M. A ; Esfarjani, K ; Sharif University of Technology
2004
Abstract
A generalized Hubbard model based on a molecular approach is used to calculate many electron wavefunctions of diamond vacancies. We have calculated the oscillator strength of the dipole transition rates from the ground states of the neutral and negatively charged vacancies. The ratio of the oscillator strengths is in very good quantitative agreement with the reported optical spectroscopic data. Electronic configurations in the ground and dipole allowed excited states are presented. With the proposed picture, the much larger oscillator strength of the negatively charged vacancy with respect to other experimentally investigated color centers N-V, H3, X3 and H4 is explained
Investigation of thrust effect on the vibrational characteristics of flexible guided missiles
, Article Journal of Sound and Vibration ; Volume 272, Issue 1-2 , 2004 , Pages 287-299 ; 0022460X (ISSN) ; Assadian, N ; Sharif University of Technology
Academic Press
2004
Abstract
In this paper the effect of thrust on the bending behaviour of flexible missiles is investigated. For this purpose, the governing equations of motion of a flexible guided missile are derived following the Lagrangian approach. The missile is idealized as a non-uniform beam where the bending elastic deflections are modelled using the method of modal substitution. The vehicle (time varying) bending modeshapes and natural frequencies are determined by modelling variable mass and stiffness distributions with thrust and mass burning effects accounted for. To solve this problem the missile is divided into several segments of uniform stiffness, density and axial force distribution. This approach...
Exact solutions for universal holonomic quantum gates
, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 70, Issue 1 , 2004 , Pages 012320-1-012320-5 ; 10502947 (ISSN) ; Majd, N ; Sharif University of Technology
American Physical Society
2004
Abstract
Implementation of local quantum gate on specific qubits in an array of qubits by carrying a Hamiltonian around a closed loop is discussed. A family of isospectral Hamiltonians with the same spectrum of the projection operator on the main array is constructed by choice of a suitable curve. For every single qubit gate acting on the k-th qubit, a local operator Xk acts nontrivially on the ancilla and the qubit. Imbedding appropriate operators for a suitable set of qubit gates comprises of a universal set of quantum gates. In tensor product of the array one can enact holonomically any set of gates on any subset of qubits
Buckling of the composite cracked cylindrical shells subjected to axial load
, Article 2003 ASME International Mechanical Engineering Congress, Washington, DC, 15 November 2003 through 21 November 2003 ; Volume 470 , 2003 , Pages 87-93 ; 0277027X (ISSN) ; Nayeb Hashemi, H ; Estekanchi, H. E ; ASME ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2003
Abstract
Cylindrical shells constitute the main structural components in pressure vessels and pipelines. Cylindrical shells made of fiber-reinforced composites are now being considered in the design of many components due to their high specific strength and stiffness. Buckling is one of the main failure considerations, when designing the cylindrical shells. The buckling behavior of the composite cylindrical shells can severely be compromised by introducing defect in the structure, due to high stress field generated around these defects. Defects could be generated during service due to cyclic loading or during manufacturing. A reliable operation of these structures require to understand the effects of...
Genetic approach to pole placement by static output feedback
, Article 2002 Congress on Evolutionary Computation, CEC 2002, Honolulu, HI, 12 May 2002 through 17 May 2002 ; Volume 2 , 2002 , Pages 1174-1179 ; 0780372824 (ISBN); 9780780372825 (ISBN) ; Kuchakkhani, S ; Sharif University of Technology
IEEE Computer Society
2002
Abstract
In this paper, a new approach for solving the problem of pole assignment, using static output feedback, has been proposed. The proposed approach is based on genetic algorithm where it can place all the closed-loop poles at desired locations with a high accuracy, provided that there exists a solution to the problem. It is also shown that how some known difficulties of static output feedback like order of system, multiplicity of the desired poles and the need for having closed-loop poles to be distinct or different from the open loop poles have been solved. Numerical examples at the end of the paper illustrate the applicability and the performance of the proposed method. © 2002 IEEE
Composite pnlms & nlms adaptation: A new method for network echo cancellation
, Article 14th International Conference on Digital Signal Processing, DSP 2002, 1 July 2002 through 3 July 2002 ; Volume 2 , 2002 , Pages 757-760 ; 0780375033 (ISBN) ; Atarodi, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2002
Abstract
This paper describes an improved version of the recently proposed fast converging algorithm. PNLMS, for network echo cancellers. We have introduced a simple analysis of the PNLMS convergence behavior to show why after the fast initial convergence, it slows down. Also, the method has been worked out to overcome this deficiency is presented. Improvement is shown by several simulation results. © 2002 IEEE
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...
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...
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...