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**Search for:**eigenvalues-and-eigenfunctions

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Total 167 records

#### Wireless multicasting using network coding

, Article 2006 1st Workshop on Operator-Assisted (Wireless-Mesh) Community Networks, OpComm 2006, Berlin, 18 September 2006 through 19 September 2006 ; 2006 ; 1424406927 (ISBN); 9781424406920 (ISBN) ; Khalaj, B. H ; Sharif University of Technology
2006

Abstract

In this paper, we consider the network coding in networks with broadcast channels (called hypernetworks) as the first step for applying network coding to wireless networks. We first prove a Max-Flow Min-Cut theorem for such networks. While we propose an algorithm to achieve this bound, we will introduce new definitions and provide sufficient tools to extend many of the theorems stated for flows in wireline networks to the case of hypernetworks. As an example, we will extend the Max-Flow Min-Cut condition for feasibility of the point-to-point connection in wireline networks to the case of hypernetworks. Then, we will extend the algebraic approach of Koetter and Medard in [3] to the...

#### Vibrations and stability analysis of double current-carrying strips interacting with magnetic field

, Article Acta Mechanica ; 2020 ; Firouz Abadi, R. D ; Sharif University of Technology
Springer
2020

Abstract

Interactive vibrations and buckling of double current-carrying strips (DCCS) are investigated in this study. Considering the rotational and transverse deformation of the strip, four coupled equations of motion are obtained using Hamilton’s principle. Using the Galerkin method, mass and stiffness matrices are extracted and the stability of the system is determined by solving the eigenvalue problem. Effects of pretension and elevated temperature on the stability of DCCS are studied for three types of materials and various arrangements. Finally, the effect of horizontal or vertical distance between strips on the critical current value is investigated. According to the results, the effects of...

#### Variational formulation on Joule heating in combined electroosmotic and pressure driven microflows

, Article International Journal of Heat and Mass Transfer ; Volume 61, Issue 1 , June , 2013 , Pages 254-265 ; 00179310 (ISSN) ; Saidi, M. H ; Waezi, Z ; Chakraborty, S ; Sharif University of Technology
2013

Abstract

The present study attempts to analyze the extended Graetz problem in combined electroosmotic and pressure driven flows in rectangular microchannels, by employing a variational formulation. Both the Joule heating and axial conduction effects are taken into consideration. Since assuming a uniform inlet temperature profile is not consistent with the existence of these effects, a step change in wall temperature is considered to represent physically conceivable thermal entrance conditions. The method of analysis considered here is primarily analytical, in which series solutions are presented for the electrical potential, velocity, and temperature. For general treatment of the eigenvalue problem...

#### Validation of a new MCNP-ORIGEN linkage program for burnup analysis

, Article Progress in Nuclear Energy ; Volume 63 , 2013 , Pages 27-33 ; 01491970 (ISSN) ; Abbaspour, A ; Pazirandeh, A ; Sharif University of Technology
2013

Abstract

The analysis of core composition changes is complicated by the fact that the time and spatial variation in isotopic composition depend on the neutron flux distribution and vice versa. Fortunately, changes in core composition occur relatively slowly and hence the burnup analysis can be performed by dividing the burnup period into some burnup spans and assuming that the averaged flux and cross sections are constant during each step. The burnup span sensitivity analysis attempts to find that how much the burnup spans could be increased without any significant deviation in results. This goal has been achieved by developing a new MCNP-ORIGEN linkage program named as MOBC (MCNP-ORIGEN Burnup...

#### UWB orthogonal pulse design using Sturm–Liouville boundary value problem

, Article Signal Processing ; Volume 159 , 2019 , Pages 147-158 ; 01651684 (ISSN) ; Mohajerin Esfahani, P ; Ghavami, M ; Marvasti, F ; Sharif University of Technology
Elsevier B.V
2019

Abstract

The problem of designing UWB pulses which meet specific spectrum requirements is usually treated by filtering common pulses such as Gaussian doublets, modified Hermite polynomials and wavelets. When there is the need to have a number of orthogonal pulses (e.g., in a multiuser scenario), a naive approach is to filter all the members of an orthogonal set, which is likely to destroy their orthogonality property. In this paper, we study the design of a set of pulses that simultaneously satisfy the orthogonality property and spectrum requirements. Our design is based on the eigenfunctions of Sturm–Liouville boundary value problems. Indeed, we introduce Sturm–Liouville differential equations for...

#### Using piezoelectric materials to control the dynamic response of a thin rectangular plate under moving mass

, Article 11th East Asia-Pacific Conference on Structural Engineering and Construction, EASEC-11, Taipei, 19 November 2008 through 21 November 2008 ; January , 2008 ; Rofooei, F. R ; Sharif University of Technology
2008

Abstract

The governing differential equation of motion for an undamped thin rectangular plate with a number of bonded piezoelectric patches on its surface, and arbitrary boundary conditions are derived using Hamilton's principle. A moving mass traveling on an arbitrary trajectory acts as an external excitation for the system. The effect of moving mass inertia is considered using all the out-of-plane translational acceleration components. The method of eigenfunction expansion is used to decouple the equation of motion into a number of coupled ordinary differential equations. A classical closed loop optimal control algorithm is employed to suppress the dynamic response of the system by determining the...

#### 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) ; 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...

#### Two-dimensional model of melt flows and interface instability in aluminum reduction cells

, Article Light Metals 2008, New Orleans, LA, 9 March 2008 through 13 March 2008 ; 2008 , Pages 443-448 ; 01470809 (ISSN); 9780873397100 (ISBN) ; Sharif University of Technology
2008

Abstract

We derive a new non-linear two dimensional model for melt flows and interface instability in aluminum reduction cells. This model is based on non-linear de St. Venant shallow water equations and contains the main features of an aluminum reduction cell. In this model we consider linear friction terms but in a new way that has not been considered in previous works. Our results are in good agreement with the results of simulation of viscous flow. This model is applicable both in determination of melt flows in molten aluminum and cryolite layers and also in finding the extreme limit for stability of interfacial waves in an aluminum reduction cell

#### True damping and frequency prediction for aeroelastic systems: The PP method

, Article Journal of Fluids and Structures ; Volume 25, Issue 7 , 2009 , Pages 1177-1188 ; 08899746 (ISSN) ; Firouz Abadi, R. D ; Sharif University of Technology
2009

Abstract

This paper presents a numerical scheme for stability analysis of the aeroelastic systems in the Laplace domain. The proposed technique, which is called the PP method, is proposed for when the aerodynamic model is represented in the Laplace domain and includes complicated transcendental expressions in terms of the Laplace variable. This method utilizes a matrix iterative procedure to find the eigenvalues of the system and generalizes the other methods such as the P and PK methods for prediction of the flutter conditions. The major advantage of this technique over the other approximate methods is true prediction of subcritical damping and frequency values of the aeroelastic modes. To examine...

#### Trees with a large Laplacian eigenvalue multiplicity

, Article Linear Algebra and Its Applications ; Volume 586 , 2020 , Pages 262-273 ; van Dam, E. R ; Fakharan, M. H ; Sharif University of Technology
Elsevier Inc
2020

Abstract

In this paper, we study the multiplicity of the Laplacian eigenvalues of trees. It is known that for trees, integer Laplacian eigenvalues larger than 1 are simple and also the multiplicity of Laplacian eigenvalue 1 has been well studied before. Here we consider the multiplicities of the other (non-integral) Laplacian eigenvalues. We give an upper bound and determine the trees of order n that have a multiplicity that is close to the upper bound [Formula presented], and emphasize the particular role of the algebraic connectivity. © 2019 Elsevier Inc

#### Towards obtaining more information from gas chromatography-mass spectrometric data of essential oils: An overview of mean field independent component analysis

, Article Journal of Chromatography A ; Volume 1217, Issue 29 , 2010 , Pages 4850-4861 ; 00219673 (ISSN) ; Parastar, H ; Sereshti, H ; Sharif University of Technology
2010

Abstract

Mean field independent component analysis (MF-ICA) along with other chemometric techniques was proposed for obtaining more information from multi-component gas chromatographic-mass spectrometric (GC-MS) signals of essential oils (mandarin and lemon as examples). Using these techniques, some fundamental problems during the GC-MS analysis of essential oils such as varying baseline, presence of different types of noise and co-elution have been solved. The parameters affecting MF-ICA algorithm were screened using a 25 factorial design. The optimum conditions for MF-ICA algorithm were followed by deconvolution of complex GC-MS peak clusters. The number of independent components (ICs) (chemical...

#### Tight bound on the stability of control systems over parallel gaussian channels using a new joint source channel coding

, Article 2019 Iran Workshop on Communication and Information Theory, IWCIT 2019, 24 April 2019 through 25 April 2019 ; 2019 ; 9781728105840 (ISBN) ; Motahari, A. S ; Farhadi, A ; Khalaj, B. H ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019

Abstract

In this paper, we address the stability problem of a noiseless linear time invariant control system over parallel Gaussian channels with feedback. It is shown that the eigenvalues-rate condition which has been proved as a necessary condition, is also sufficient for stability over parallel Gaussian channels. In fact, it is proved that for stabilizing a control system over the parallel Gaussian channels, it suffices that the Shannon channel capacity obtained by the water filling technique is greater than the sum of the logarithm of the unstable eigenvalues magnitude. In order to prove this sufficient condition, we propose a new nonlinear joint source channel coding for parallel Gaussian...

#### 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...

#### Thermally developing electroosmotic flow of power-law fluids in a parallel plate microchannel

, Article International Journal of Thermal Sciences ; Volume 61 , 2012 , Pages 106-117 ; 12900729 (ISSN) ; Saidi, M.H ; Veisi, H ; Fattahi, M ; Sharif University of Technology
2012

Abstract

The present investigation considers the thermally developing electroosmotic flow of power-law fluids through a parallel plate microchannel. Both the viscous dissipation and Joule heating effects are taken into account and a step change in wall temperature is considered to represent physically conceivable thermal entrance conditions. Expressions for the dimensionless temperature and Nusselt number in the form of infinite series are presented. In general, the resultant eigenvalue problem is solved numerically; nevertheless, an analytical solution is presented for the regions close to the entrance. A parametric study reveals that increasing amounts of the Peclet number result in higher wall...

#### Theoretical and experimental analysis of the free vibrations of a shell made of n cone segments joined together

, Article Thin-Walled Structures ; Volume 108 , 2016 , Pages 416-427 ; 02638231 (ISSN) ; Saadat Foumani, M ; Navazi, H. M ; Sharif University of Technology
Elsevier Ltd

Abstract

This paper investigates the free vibrations of a shell made of n cone segments joined together. The governing equations of the conical shell were obtained by applying the Sanders shell theory and the Hamilton principle. Then, these governing equations are solved by using the power series method and considering a displacement field which is harmonic function about the time and the circumferential coordinate. Using the boundary conditions of the two ends of the shell and the continuity conditions at the interface section of shell segments, and solving the eigenvalue problem, the natural frequencies and the mode shapes are obtained. Very good agreements exist between the analytical results of...

#### 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

#### The main eigenvalues of signed graphs

, Article Linear Algebra and Its Applications ; 2020 ; 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

#### 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) ; 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...

#### 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...

#### 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...