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#### A novel graphical approach to automatic abstraction in reinforcement learning

, Article Robotics and Autonomous Systems ; Volume 61, Issue 8 , 2013 , Pages 821-835 ; 09218890 (ISSN) ; Beigy, H ; Sharif University of Technology
2013

Abstract

Recent researches on automatic skill acquisition in reinforcement learning have focused on subgoal discovery methods. Among them, algorithms based on graph partitioning have achieved higher performance. In this paper, we propose a new automatic skill acquisition framework based on graph partitioning approach. The main steps of this framework are identifying subgoals and discovering useful skills. We propose two subgoal discovery algorithms, which use spectral analysis on the transition graph of the learning agent. The first proposed algorithm, incorporates k′-means algorithm with spectral clustering. In the second algorithm, eigenvector centrality measure is utilized and options are...

#### Limiting spectral distribution of the sample covariance matrix of the windowed array data

, Article Eurasip Journal on Advances in Signal Processing ; Volume 2013, Issue 1 , 2013 ; 16876172 (ISSN) ; Gazor, S ; Bastani, M. H ; Sharif University of Technology
2013

Abstract

In this article, we investigate the limiting spectral distribution of the sample covariance matrix (SCM) of weighted/windowed complex data. We use recent advances in random matrix theory and describe the distribution of eigenvalues of the doubly correlated Wishart matrices. We obtain an approximation for the spectral distribution of the SCM obtained from windowed data. We also determine a condition on the coefficients of the window, under which the fragmentation of the support of noise eigenvalues can be avoided, in the noise-only data case. For the commonly used exponential window, we derive an explicit expression for the l.s.d of the noise-only data. In addition, we present a method to...

#### 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) ; 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...

#### Asymptotic eigenvectors, topological patterns and recurrent networks

, Article Proceedings of the Romanian Academy Series A - Mathematics Physics Technical Sciences Information Science ; Volume 14, Issue 2 , 2013 , Pages 95-100 ; 14549069 (ISSN) ; Sharif University of Technology
2013

Abstract

The notions of asymptotic eigenvectors and asymptotic eigenvalues are defined. Based on these notions a special probability rule for pattern selection in a Hopfield type dynamics is introduced. The underlying network is considered to be a d-regular graph, where d is an integer denoting the number of nodes connected to each neuron. It is shown that as far as the degree d is less than a critical value dc, the number of stored patterns with m μ = O(1) can be much larger than that in a standard recurrent network with Bernouill random patterns. As observed in [4] the probability rule we study here turns out to be related to the spontaneous activity of the network. So our result might be an...

#### 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...

#### Interaction of the dynamics of doubly fed wind generators with power system electromechanical oscillations

, Article IET Renewable Power Generation ; Volume 7, Issue 2 , March , 2013 , Pages 89-97 ; 17521416 (ISSN) ; Ranjbar, A. M ; Sharif University of Technology
2013

Abstract

The interaction of the dynamics of doubly fed wind generators with the electromechanical mode of nearby synchronous generators (SGs) can affect the small signal stability of power systems with high penetration levels of wind power. In this study, a novel approach is developed to investigate these interactions and their impact on the damping of power system oscillations. In this approach it is not necessary to model the dynamic behaviour of system SGs and only the frequencies of system oscillations are important. This approach is based on the sensitivity of SGs electromechanical eigenvalue with respect to variations in the Jacobian matrix of power system. By applying this approach to a test...

#### Seepage analysis in multi-domain general anisotropic media by three-dimensional boundary elements

, Article Engineering Analysis with Boundary Elements ; Volume 37, Issue 3 , 2013 , Pages 527-541 ; 09557997 (ISSN) ; Ataie Ashtiani, B ; Sharif University of Technology
2013

Abstract

A three-dimensio111nal boundary element solution for the seepage analysis in multi-domain general anisotropic media has been developed based on the transformation approach. Using analytical eigenvalues and eigenvectors of the hydraulic conductivity tensor, a closed-form coordinate transformation matrix has been provided to transform the quadratic form of governing equation of seepage for the general anisotropic media to the Laplace equation. This transformation allows the analysis to be carried out using any standard BEM codes for the potential theory on the transformed space by adding small pre- and post-processing routines. With this transformation, any physical quantity like the total...

#### 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...

#### Electroosmotic flow of viscoelastic fluids through a slit microchannel with a step change in wall temperature

, Article Journal of Heat Transfer ; Volume 135, Issue 2 , 2013 ; 00221481 (ISSN) ; Veisi, H ; Saidi, M. H ; Asghar Mozafari, A ; Sharif University of Technology
2013

Abstract

Thermally developing electroosmotically generated flow of two viscoelastic fluids, namely the PTT and FENE-P models, through a slit microchannel is considered. 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...

#### A successive boundary element model for investigation of sloshing frequencies in axisymmetric multi baffled containers

, Article Engineering Analysis with Boundary Elements ; Volume 37, Issue 2 , 2013 , Pages 383-392 ; 09557997 (ISSN) ; Noorian, M. A ; Haddadpour, H ; Sharif University of Technology
2013

Abstract

This study presents a developed successive Boundary Element Method to determine the symmetric and antisymmetric sloshing natural frequencies and mode shapes for multi baffled axisymmetric containers with arbitrary geometries. The developed fluid model is based on the Laplace equation and Green's theorem. The governing equations of fluid dynamic and free surface boundary condition are also applied to proposed model. A zoning method is presented to model arbitrary arrangement of baffles in multi baffled axisymmetric tanks. The influence of each zone on neighboring zones is applied by introducing interface influence matrix which correlates the velocity potential of interfaces to their flux. By...

#### 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...

#### Out-of-plane buckling of Y-braced frames with rigid joints

, Article Proceedings of the Institution of Civil Engineers: Structures and Buildings ; Volume 166, Issue 1 , 2013 , Pages 28-37 ; 09650911 (ISSN) ; Vafai, A ; Kazemi, M.T ; Sharif University of Technology
2013

Abstract

Because of the complicated buckling characteristics of Y-shaped bracings, calculation of their strength is beyond routine engineering procedures. A method based on slope-deflection equations incorporating stability functions has been used for computation of buckling eigenvalues and effective length factors. Lateral strength is computed based on the least buckling strength of bracing members. This study is limited to bracings with similar sections and fixed end connections resisting out-of-plane rotation. Lateral strengths predicted by the analytical method for two cases are compared with experimental results on full-scale specimens. It is shown that the proposed analytical method predicts...

#### Development of two-dimensional, multigroup neutron diffusion computer code based on GFEM with unstructured triangle elements

, Article Annals of Nuclear Energy ; Volume 51 , 2013 , Pages 213-226 ; 03064549 (ISSN) ; Vosoughi, N ; Sharif University of Technology
2013

Abstract

Various methods for solving the forward/adjoint equation in hexagonal and rectangular geometries are known in the literatures. In this paper, the solution of multigroup forward/adjoint equation using Finite Element Method (FEM) for hexagonal and rectangular reactor cores is reported. The spatial discretization of equations is based on Galerkin FEM (GFEM) using unstructured triangle elements. Calculations are performed for both linear and quadratic approximations of the shape function; based on which results are compared. Using power iteration method for the forward and adjoint calculations, the forward and adjoint fluxes with the corresponding eigenvalues are obtained. The results are then...

#### A VLSI architecture for multiple antenna eigenvalue-based spectrum sensing

, Article 2012 19th IEEE International Conference on Electronics, Circuits, and Systems, ICECS 2012, 9 December 2012 through 12 December 2012 ; December , 2012 , Pages 153-156 ; 9781467312615 (ISBN) ; Shabany, M ; Sharif University of Technology
2012

Abstract

An Eigenvalue-based detection (EBD) scheme, is proposed as an efficient method to overcome the noise uncertainty and the SNR wall problem in conventional energy detection (ED) schemes. Despite remarkable efforts made to analyze the EBD performance, a VLSI implementation is missing in literature. In this paper, a new FFT-based EBD algorithm is introduced, which eliminates the need for filter banks and discrete wavelet packet transform to channelize the input signal. The proposed method enables the utilization of the EBD algorithm in high-resolution spectrum sensing approaches. Moreover, it enables the detection of signals with SNRs as low as -10 dB. A low-power, area-efficient yet real-time...

#### Neutron noise simulation by GFEM and unstructured triangle elements

, Article Nuclear Engineering and Design ; Volume 253 , 2012 , Pages 238-258 ; 00295493 (ISSN) ; Vosoughi, N ; Sharif University of Technology
2012

Abstract

In the present study, the neutron noise, i.e. The stationary fluctuation of the neutron flux around its mean value, is calculated in 2-group forward and adjoint diffusion theory for both hexagonal and rectangular reactor cores. To this end, the static neutron calculation is performed at the first stage. The spatial discretization of equations is based on linear approximation of Galerkin Finite Element Method (GFEM) using unstructured triangle elements. Using power iteration method, forward and adjoint fluxes with the corresponding eigenvalues are obtained. The results are then benchmarked against the valid results for BIBLIS-2D and IAEA-2D benchmark problems and DONJON computer code. The...

#### Application of subsynchronous damping controller (SSDC) to STATCOM

, Article International Journal of Electrical Power and Energy Systems ; Volume 43, Issue 1 , December , 2012 , Pages 418-426 ; 01420615 (ISSN) ; Mozaffari, B ; Ranjbar, A. M ; Sharif University of Technology
2012

Abstract

In this paper a novel supplementary subsynchronous damping controller (SSDC) is proposed for the STATic synchronous COMpensator (STATCOM) which is capable of damping out subsynchronous oscillations in power system with series compensated transmission lines. An auxiliary subsynchronous damping controller (SSDC) for a STATCOM using the generator rotor speed deviation signal as the stabilizing signal has been designed to damp subsynchronous oscillations. Eigenvalue analysis and transient simulations of detailed nonlinear system are considered to investigate the performance of the controller. Robustness of the controller has been analyzed by facing the system with disturbances leading to...

#### Source enumeration in large arrays based on moments of eigenvalues in sample starved conditions

, Article IEEE Workshop on Signal Processing Systems, SiPS: Design and Implementation, 17 October 2012 through 19 October 2012, Quebec ; October , 2012 , Pages 79-84 ; 15206130 (ISSN) ; 9780769548562 (ISBN) ; Bastani, M. H ; Gazor, S ; Sharif University of Technology
2012

Abstract

This paper presents a scheme to enumerate the incident waves impinging on a high dimensional uniform linear array using relatively few samples. The approach is based on Minimum Description Length (MDL) criteria and statistical properties of eigenvalues of the Sample Covariance Matrix (SCM). We assume that several models, with each model representing a certain number of sources, will compete and MDL criterion will select the best model with the minimum model complexity and maximum model decision. Statistics of noise eigenvalue of SCM can be approximated by the distributional properties of the eigenvalues given by Marcenko-Pastur distribution in the signal-free SCM. In this paper we use random...

#### New sufficient conditions for robust stability analysis of interval matrices

, Article Systems and Control Letters ; Volume 61, Issue 12 , 2012 , Pages 1117-1123 ; 01676911 (ISSN) ; Babazadeh, M ; Karimi, H ; Nobakhti, A ; Sharif University of Technology
2012

Abstract

This letter presents new sufficient conditions for robust Hurwitz stability of interval matrices. The proposed conditions are based on two approaches: (i) finding a common Lyapunov matrix for the interval family and (ii) converting the robust stability problem into a robust non-singularity problem using Kronecker operations. The main contribution of the letter is to derive accurate and computationally simple optimal estimates of the robustness margin and spectral bound of general interval matrices. The evaluation of the condition relies on the solutions of linear matrix inequalities (LMIs) and eigenvalue problems, both of which are solved very efficiently. The improvements gained by using...

#### 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...

#### 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) ; 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