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  • The PageRank algorithm for determining the importance of Web pages has become a central technique in Web search. This algorithm uses the Power method to compute successive iterates that converge to the principal eigenvector of the Markov chain representing the Web link graph. In this work we present an effective heuristic Relaxed and Extrapolated algorithm based on the Power method that accelerates its convergence. A hybrid parallel implementation of this algorithm has been designed by combining various OpenMP threads for each MPI process and several strategies of data distribution among nodes have been analyzed. The results show that the proposed algorithm can significantly speed up the convergence time with respect to the parallel Power algorithm.
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  • We analyze temporal variations of two solar indices, the monthly mean Maximum CME Speed Index (MCMESI) and the International Sunspot Number (ISSN) as well as the monthly median ionospheric critical frequencies (foF1, and foF2) for the time period of 1996–2013, which covers the entire solar cycle 23 and the ascending branch of the cycle 24. We found that the maximum of foF1 and foF2 occurred respectively during the first and second maximum of the ISSN solar activity index in the solar cycle 23. We compared these data sets by using the cross-correlation and hysteresis analysis and found that both foF1 and foF2 show higher correlation with ISSN than the MCMESI during the investigated time period, but when significance levels are considered correlation coefficients between the same indices become comparable. Cross-correlation analysis showed that the agreement between these data sets (solar indices and ionospheric critical frequencies) is better pronounced during the ascending phases of solar cycles, while they display significant deviations during the descending phase. We conclude that there exists a signature of a possible relationship between MCMESI and foF1 and foF2, which means that MCMESI could be used as a possible indicator of solar and geomagnetic activity, even though other investigations are needed.
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  • Gas mixture flows take place in a wide range of scientific and technical problems, including space applications, microchannel streams, nanotechnology and others. This paper deals with numerical simulation of gas mixture flows in microchannels. For such flows speeds can have supersonic, subsonic and transonic ranges according to parameters of gas stream and properties. The supersonic expansion of gas mixtures is accompanied by several simultaneous nonequilibrium processes: interfusion of layers, shock waves, heat exchange with walls etc. To investigate these complex problems, it is essential to develop adequate numerical technique that contains stable and robust numerical algorithms and calculations based on fine grids. These calculations are supposed to be carried out by means of high performance computer systems.
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  • In the present paper, the interface fracture toughness between a Ti coating film and Al-alloy substrate is evaluated using a laser spallation method and a boundary element method. The fracture toughness can be estimated using inverse analyses by the boundary element method using a transfer function computed from the history of the displacement of the specimen. In the present study, an alternative boundary element program is developed for unsteady state vibration of an axi-symmetric solid body. The mode I interface fracture toughness between the Ti coating film and Al-alloy substrate is confirmed to be about 0.66 MPam1/2 from the present investigation.
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  • Reactive power planning (RPP) is generally defined as an optimal allocation of additional reactive power sources that should be installed in the network for a predefined horizon of planning at minimum cost while satisfying equality and inequality constraints. The optimal placements of new VAR sources can be selected according to certain indices related to the objectives to be studied. In this paper, various solution methods for solving the RPP problem are extensively reviewed which are generally categorized into analytical approaches, arithmetic programming approaches, and meta-heuristic optimization techniques. The research focuses on the disparate applications of meta-heuristic algorithms for solving the RPP problem. They are subcategorized into evolution based, and swarm intelligence. Also, a study is performed via the multi-objective formulations of reactive power planning and operations to clarify their merits and demerits.
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  • Magnetohydrodynamic (MHD) stagnation point flow and heat transfer problem from a stretching sheet in the presence of a heat source/sink and suction/injection in porous media is studied in this paper. The governing partial differential equations are solved using the Chebyshev spectral method based perturbation approach. The method, namely the spectral perturbation method (SPM), is a series expansion technique which extends the use of the standard perturbation approach by coupling it with the Chebyshev pseudo-spectral method. Series solutions for small velocity ratio and asymptotic solutions for large velocity ratio are generated and the results are also validated against those obtained using the spectral quasi-linearisation method (SQLM). It is seen from this study that the SPM can be used as an alternative approach to find numerical solutions for complicated expansions encountered in perturbation schemes. The results are benchmarked with previously published results.
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  • This paper introduces a new powerful evolutionary algorithm called backtracking search algorithm (BSA) for solving load frequency control (LFC) problem in power system. Initially, two-area non-reheat thermal power plant is considered and gains of PI/PID controllers are optimized using BSA. This paper compares BSA’s effectiveness in solving LFC problem with the performances of other optimization techniques reported in the literature. Nonlinearities of power system such as reheater, governor dead band, boiler dynamics and generation rate constraint are included in the system modeling to identify the system stability and its performance is compared with craziness based PSO technique. Additionally, two more test systems namely three-area and four-area hydro-thermal plant with nonlinearity are considered to demonstrate the efficiency of proposed algorithm. The comparative analysis of the performances indicates that the proposed controller gives better results than other techniques available in the literature. Sensitivity analysis showed robustness of proposed controller under loading and parameter uncertainty.
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  • The integration of distributed generation (DG) in distribution network may significantly affect its performance. Transmission networks are no longer accountable solely for voltage security issues in distribution networks with penetration of DGs. The reactive power support from the DG sources greatly varies with the type of DG units and may potentially distress the larger portion of the network from the voltage stability aspects. This paper presents the analysis for the selection of the best type of DG unit among different categories and its optimal location that can enhance the voltage stability of distribution network with simultaneous improvement in voltage profile. Voltage sensitivity index and bus participation factors derived from continuation power flow and Modal Analysis, respectively, are used together for voltage stability assessment and placement of DGs. Changes in mode shapes and participation factors with the placement of DGs are comprehensively analyzed for 33 and 136 nodes radial distribution network.
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  • In this study, the entropy generation of micropolar fluid flow through concentric cylindrical annulus associated with slip and convective boundary conditions is performed numerically. The fluid flow in an annulus is due to the rotation of the outer cylinder with constant velocity. The analysis of such kind of fluid flow is governed by nonlinear partial differential equations. In the present study these equations are solved using the spectral quasilinearization method. The resultant velocity, microrotation and temperature distributions from the spectral quasi linearization method are used to evaluate the entropy generation rate and the Bejan number. Further the impact of boundary conditions on the entropy generation is also presented.
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  • Post-treatment methods enhance the fatigue strength of welded high-strength steel joints significantly. In industrial applications, one commonly applied technique is the high frequency mechanical impact (HFMI) treatment. Attained local benefits increasing fatigue strength are the compressive residual stress state, the reduced notch effect at the weld toe, and additionally the local work hardening of the material. This paper presents the set-up of a closed simulation loop including structural weld simulation, numerical computation of the HFMI-process, and a numerical evaluation of the local fatigue life.
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