Contributors:Tamoghna Purkayastha, Debashis De, Tanay Chattopadhyay
Quantum-dot Cellular Automata (QCA) demands to be a promising alternative of CMOS in ultra large scale circuit integration. Arithmetic and logic unit designs using QCA are of high research interest. A layout of four and eight bit universal shift register (USR) has been proposed. Initially QCA layouts of D flip-flop with clear and 4 to 1 multiplexer are designed, which are extended to design 4 and 8-bit parallel in parallel out (PIPO) shift register. Finally the PIPO is utilized to design 4-bit and 8-bit USR. By the comparative analysis it is observed that the proposed D Flip-flop achieved 40% clock delay improvement, whereas the modified layout of 4 to 1 multiplexer achieved 30% cell count reduction and 17% clock delay reduction from the previous works. This results in 31% reduction in cell count, 45% reduction in area and 55% reduction in clock cycle delay in 8 bit USR layout.
In this paper, an optimal design of linear phase digital finite impulse response (FIR) band stop (BS) filter using the L1-norm based real-coded genetic algorithm (L1-RCGA) is presented. Although RCGA has proved its ability to overcome the drawbacks associated with conventional gradient-based optimization methods of filter design, it is applied here with a novel fitness function based on the L1-norm. This leads to a global optimal solution along with the improvement in filter design with same specifications. The designed filter pursues a better response in terms of flat passband, high stopband attenuation and fast convergence. The simulation results justify that the proposed FIR BS filter using L1-RCGA outperforms the existing optimization techniques, the L1-method and particle swarm optimization (PSO) and the conventional methods such as least-squares (LS) approach, Kaiser window method and the Parks McClellan (PM) algorithm. A detailed analysis is performed to evaluate the performance of the designed filters.
Contributors:Héctor Migallón, Violeta Migallón, Juan A. Palomino, José Penadés
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.
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.
Contributors:T. Kudryashova, Yu. Karamzin, V. Podryga, S. Polyakov
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.
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.
In the paper a general and direct method for implementation of influence lines in finite element software is provided. Generally influence lines are applied to identify the most critical location and combination of live loads in civil engineering structures. The proposed method is based on the Müller-Breslau principle and the basic idea is to equate discontinuous displacement fields with consistent nodal forces, thus obtaining influence functions only applying a single load case without changing the geometry or boundary conditions of the finite element model. Initially the method is developed by means of some illustrative beam problems, where the consistent nodal forces for angular, lateral and axial displacement discontinuities for a Bernoulli-Euler beam element are derived. Finally it is shown that the method is fully general and efficient in identifying the influence functions of generalized stresses in e.g. plates and shells.
Contributors:Abdullah M. Shaheen, Shimaa R. Spea, Sobhy M. Farrag, Mohammed A. Abido
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.
In this paper, using a recently developed unified approach, benchmark results are presented for structural optimization when the only source of uncertainty is the variability of the applied load directions. The worst-load-direction oriented framework can be applied to a broad class of engineering optimization problems. In each case, the central element of the solution searching algorithm is a standard multi-load structure optimization problem, which using an appropriate method, can be solved within reasonable time. The varying load directions are handled by additional linear or nonlinear relations, which describe the allowable perturbations of the nominal load directions. The result of the optimization is a performance measure minimal design which is invariant to the investigated uncertainty type and satisfies the response constraints. In order to illustrate the viability and efficiency of the approach, problem-specific models, algorithms and detailed benchmark results are presented for volume minimization of 2D continuum structures with compliance constraints and weight minimization of 2D truss structures with displacement and stress constraints. In each case, the computational cost of the proposed approach is comparable with its fixed load direction oriented equivalent because the worst-load-direction identification process is searching on the space of allowable direction perturbations, which generally means an easier and smaller computational problem than the standard multi-load structure optimization.
Contributors:T.M. Agbaje, S. Mondal, Z.G. Makukula, S.S. Motsa, P. Sibanda
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.