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    Analytic performance comparison of hypercubes and star graphs with implementation constraints

    , Article Journal of Computer and System Sciences ; Volume 74, Issue 6 , September , 2008 , Pages 1000-1012 ; 00220000 (ISSN) Kiasari, A. E ; Sarbazi Azad, H ; Sharif University of Technology
    Many theoretical-based comparison studies, relying on graph structural and algorithmic properties, have been conducted for the hypercube and the star graph. None of these studies, however, have considered real working conditions and implementation limits. We have compared the performance of the star and hypercube networks for different message lengths and number of virtual channels, and considered two implementation constraints, namely the constant bisection bandwidth and constant node pin-out. We use two accurate analytical models, already proposed for the star graph and hypercube, and implement the parameter changes imposed by technological implementation constraints. When no constraint is... 

    Simulation of a density current turbulent flow employing different RANS models: a comparison study

    , Article Scientia Iranica ; Volume 16, Issue 1 , 2009 , Pages 53-63 ; 10263098 (ISSN) Mehdizadeh, A ; Firoozabadi, B ; Sharif University of Technology
    The accuracy of Reynolds Averaged Navier-Stokes (RANS) turbulence models to predict the behavior of 2-D density currents has been examined. In this work, a steady density current is simulated by the k - ε, k - ε RNG, two-layer k - ε and modified v̄2 - f model, all of which are compared with the experimental data. Density currents, with a uniform velocity and concentration, enter a channel via a sluice gate into a lighter ambient fluid and move forward down-slope. The eddy-viscosity concept cannot accurately simulate this flow because of two stress production structures found within it. Results show that all isotropic models have a weak outcome on this current, but by improving the ability of... 

    A hybrid method of artificial neural networks and simulated annealing in monitoring auto-correlated multi-attribute processes

    , Article International Journal of Advanced Manufacturing Technology ; Volume 56, Issue 5-8 , 2011 , Pages 777-788 ; 02683768 (ISSN) Niaki, S. T. A ; Akbari Nasaji, S ; Sharif University of Technology
    The quality characteristics of both manufacturing and service industries include not only the variables but the attributes as well. While a substantial research have been performed on auto-correlated variables, little attempt has been fulfilled for auto-correlated attributes. Ignoring the imbedded autocorrelation structure in constructing control charts cause not only the in-control run length to decrease, but also the false alarms to increase. To overcome these shortcomings, in this research, an autoregressive vector first models the autocorrelation structure of the process data. Then, a modified Elman neural network is developed to generate simulated data using the ARTA algorithm. Next, a... 

    A hybrid variable neighborhood search and simulated annealing algorithm to estimate the three parameters of the Weibull distribution

    , Article Expert Systems with Applications ; Volume 38, Issue 1 , January , 2011 , Pages 700-708 ; 09574174 (ISSN) Abbasi, B ; Niaki, S. T. A ; Khalife, M. A ; Faize, Y ; Sharif University of Technology
    The Weibull distribution plays an important role in failure distribution modeling of reliability research. While there are three parameters in the general form of this distribution, for simplicity, one of its parameters is usually omitted and as a result, the others are estimated easily. However, due to its more flexibility, when the general form of the Weibull distribution is of interest, the estimation procedure is not an easy task anymore. For example, in the maximum likelihood estimation method, the likelihood function that is formed for a three-parameter Weibull distribution is very hard to maximize. In this paper, a new hybrid methodology based on a variable neighborhood search and a... 

    Dynamic analysis of a functionally graded simply supported Euler-Bernoulli beam subjected to a moving oscillator

    , Article Acta Mechanica ; Volume 224, Issue 2 , 2013 , Pages 425-446 ; 00015970 (ISSN) Rajabi, K ; Kargarnovin, M. H ; Gharini, M ; Sharif University of Technology
    The dynamic behavior of a functionally graded (FG) simply supported Euler-Bernoulli beam subjected to a moving oscillator has been investigated in this paper. The Young's modulus and the mass density of the FG beam vary continuously in the thickness direction according to the power-law model. The system of equations of motion is derived by using Hamilton's principle. By employing Petrov-Galerkin method, the system of fourth-order partial differential equations of motion has been reduced to a system of second-order ordinary differential equations. The resulting equations are solved using Runge-Kutta numerical scheme. In this study, the effect of the various parameters such as power-law... 

    Role of precursors and coating polymers in sol-gel chemistry toward enhanced selectivity and efficiency in solid phase microextraction

    , Article Analytica Chimica Acta ; Volume 742 , 2012 , Pages 45-53 ; 00032670 (ISSN) Bagheri, H ; Piri Moghadam, H ; Ahdi, T ; Sharif University of Technology
    Elsevier  2012
    To evaluate the selectivity and efficiency of solid phase microextraction (SPME) fiber coatings, synthesized by sol-gel technology, roles of precursors and coating polymers were extensively investigated. An on-line combination of capillary microextraction (CME) technique and high performance liquid chromatography (HPLC) was set up to perform the investigation. Ten different fiber coatings were synthesized in which five of them contained only the precursor and the rests were prepared using both the precursor and coating polymer. All the coatings were chemically bonded to the inner surface of copper tubes, intended to be used as the CME device and already functionalized by self-assembly...