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Total 234 records

    Active brownian particles and run-and-tumble particles separate inside a maze

    , Article Scientific Reports ; Volume 6 , 2016 ; 20452322 (ISSN) Khatami, M ; Wolff, K ; Pohl, O ; Ejtehadi, M. R ; Stark, H ; Sharif University of Technology
    Nature Publishing Group  2016
    Abstract
    A diverse range of natural and artificial self-propelled particles are known and are used nowadays. Among them, active Brownian particles (ABPs) and run-and-tumble particles (RTPs) are two important classes. We numerically study non-interacting ABPs and RTPs strongly confined to different maze geometries in two dimensions. We demonstrate that by means of geometrical confinement alone, ABPs are separable from RTPs. By investigating Matryoshka-like mazes with nested shells, we show that a circular maze has the best filtration efficiency. Results on the mean first-passage time reveal that ABPs escape faster from the center of the maze, while RTPs reach the center from the rim more easily.... 

    Stability of a predator-prey system with prey taxis in a general class of functional responses

    , Article Acta Mathematica Scientia ; Volume 36, Issue 1 , 2016 , Pages 62-72 ; 02529602 (ISSN) Yousefnezhad, M ; Mohammadi, S. A ; Sharif University of Technology
    Elsevier  2016
    Abstract
    In this paper, a diffusive predator-prey system with general functional responses and prey-tactic sensitivities is studied. Providing such generality, we construct a Lyapunov function and we show that the positive constant steady state is locally and globally asymptotically stable. With an eye on the biological interpretations, a numerical simulation is performed to illustrate the feasibility of the analytical findings  

    Effect of different parameters on steady state and monotonic liquefaction of gravelly soils

    , Article Geotechnical Special Publication, 17 March 2015 through 21 March 2015 ; Volume GSP 256 , March , 2015 , Pages 2034-2048 ; 08950563 (ISSN) ; 9780784479087 (ISBN) Payan, M ; Ayoubi, P ; Mirmo'Azen, S. M ; Sharif University of Technology
    American Society of Civil Engineers (ASCE)  2015
    Abstract
    In the current research, the main concern is to verify the behavior of gravelly soils. To that matter, with taking use of CU triaxial tests and variations in parameters of interest, gradation, relative density, isotropic pressure and anisotropy of consolidation during the tests, the effects on the steady state condition and monotonic liquefaction of gravelly soils are investigated. The test results indicated that as the isotropic pressure increases, percentage increase of steady state strength resulting from the increase of relative density will decrease. Moreover, with the increase of anisotropy of consolidation, the effect of relative density on steady state strength and built-up pore... 

    Derivation of a low-frequency model for a 3D wound core transformer

    , Article 2017 25th Iranian Conference on Electrical Engineering, ICEE 2017, 2 May 2017 through 4 May 2017 ; 2017 , Pages 1319-1323 ; 9781509059638 (ISBN) Elhaminia, P ; Hajipour, E ; Moradnouri, A ; Vakilian, M ; Sharif University of Technology
    Abstract
    3D wound core is a newly proposed core structure, which is used for construction of distribution transformers. Although many advantages have been proposed for transformer with 3D wound core and it has found increasing application in some countries such as China and Iran, no model has been presented so far in the literature for such transformers. In this paper, a low frequency model, derived based on the duality principle for transformer with 3D wound core, which can be used for both steady state and low-frequency transient studies. The validity of the model in steady state condition is then verified by experimental results. © 2017 IEEE  

    Adolf Grünbaum on the steady-state theory and Creatio continua of matter out of nothing

    , Article Zygon ; Volume 46, Issue 4 , 2011 , Pages 857-871 ; 05912385 (ISSN) Karimi, M. M ; Sharif University of Technology
    Abstract
    The ideas of creatio ex nihilo of the universe and creatio continua of new matter out of nothing entered the arena of natural science with the advent of the Big Bang and the steady-state theories in the mid-twentieth century. Adolf Grünbaum has tried to interpret the steady-state theory in such a way, to show that the continuous formation of new matter out of nothing in this theory can be explained purely physically. In this paper, however, it will be shown that Grünbaum's interpretation encounters at least three problems: not distinguishing between material and efficient causes, inconsistency, and misconceiving the law of density conservation  

    Estimating the properties of naturally fractured reservoirs using rate transient decline curve analysis

    , Article Journal of Earth Science ; Volume 28, Issue 5 , 2017 , Pages 848-856 ; 1674487X (ISSN) Daryasafar, A ; Joukar, M ; Fathinasab, M ; Da Prat, G ; Kharrat, R ; Sharif University of Technology
    Abstract
    Transient rate decline curve analysis for constant pressure production is presented in this paper for a naturally fractured reservoir. This approach is based on exponential and constant bottom-hole pressure solution. Based on this method, when ln (flow rate) is plotted versus time, two straight lines are obtained which can be used for estimating different parameters of a naturally fractured reservoir. Parameters such as storage capacity ratio (ω), reservoir drainage area (A), reservoir shape factor (CA), fracture permeability (kf), interporosity flow parameter (λ) and the other parameters can be determined by this approach. The equations are based on a model originally presented by Warren... 

    A closed-form equation for steady-state availability of cold standby repairable k-out-of-n: G systems

    , Article International Journal of Quality and Reliability Management ; Volume 37, Issue 1 , 2019 , Pages 145-155 ; 0265671X (ISSN) Yaghoubi, A ; Akhavan Niaki, S. T ; Rostamzadeh, H ; Sharif University of Technology
    Emerald Group Publishing Ltd  2019
    Abstract
    Purpose: The purpose of this paper is to derive a closed-form expression for the steady-state availability of a cold standby repairable k-out-of-n system. This makes the availability calculation much easier and accurate. Design/methodology/approach: Assuming exponential distributions for system failure and repair, the Markov method is employed to derive the formula. Findings: The proposed formula establishes an easier and faster venue and provides accurate steady-state availability. Research limitations/implications: The formula is valid for the case when the probability density function of the component failure and the repair is exponential. Originality/value: The Markov method has never... 

    Theoretical modeling and optimizing design of a packaged liquid chiller

    , Article 2007 ASME/JSME Thermal Engineering Summer Heat Transfer Conference, HT 2007, Vancouver, BC, 8 July 2007 through 12 July 2007 ; July , 2007 , Pages 527-537 ; 0791842746 (ISBN); 9780791842744 (ISBN) Heydari, A ; Kargar, S ; Sharif University of Technology
    2007
    Abstract
    This work attempts to develop a physical simulation model for the purpose of studying the effect of various design parameters on the performance of a packaged liquid chiller. A computer model which simulates the steady-state cyclic performance of a vapor compression chiller is developed for the purpose of performing detailed physical design analysis of actual industrial chillers. The model can be used for optimizing design and for detailed energy efficiency analysis of packaged liquid chillers. The simulation model takes into account presence of all chiller components such as compressor, shell-and-tube condenser and evaporator heat exchangers, thermostatic expansion valve and connection... 

    Performance prediction of twin-entry turbocharger turbines

    , Article Proceedings of the ASME Turbo Expo 2002; Aircraft Engine, Coal, Biomass and Alternative Fuels, Combustion and Fuels, Education, Electric Power, Vehicular and Small Turbomachines, Amsterdam, 3 June 2002 through 6 June 2002 ; Volume 1 , 2002 , Pages 1087-1095 Ghasemi, S ; Shirani, E ; Hajilouy Benisi, A ; The International Gas Turbine Institute ; Sharif University of Technology
    2002
    Abstract
    In this paper, the performance of the twin-entry radial flow turbine under steady state and partial admission conditions is modeled. The method, which is developed here, is based on one-dimensional performance prediction. In one-dimensional modeling, the flow properties are assumed constant on a plane normal to the flow direction. This assumption is in contrast with the flow at the rotor entry of a twin-entry turbine under partial admission condition. In this study the one-dimensional performance prediction method for single-entry turbine is modified to analyze the twin-entry turbine. In particular, the loss coefficients due to friction, clearance and blade loading, which are already... 

    Design and implementation of TSC type SVC using a new approach for electrical quantities measurement

    , Article 2001 IEEE Porto Power Tech Conference, Porto, 10 September 2001 through 13 September 2001 ; Volume 2 , 2001 , Pages 262-267 ; 0780371399 (ISBN); 9780780371392 (ISBN) Tabandeh, M ; Alavi, M. H ; Marami, M ; Dehnavi, G. R ; Sharif University of Technology
    2001
    Abstract
    In this paper, a compact algorithm for balancing the load and correction of power factor in three-phase three-wire system is presented. Susceptances of SVC in each phase are computed as a function of real and imaginary parts of line current. This calculation is based on unity power factor and elimination of negative sequence of currents. A laboratory prototype of Thyristor Switched Capacitor (TSC) at 380V and 45KVAR is designed and implemented. Also, a new approach for measuring active and reactive power, power factor and voltage is presented. This measuring technique is based on integration of current signal over a specific part of voltage signal period. Finally, a brief description of... 

    Adaptive CFAR processor for nonhomogeneous environments

    , Article IEEE Transactions on Aerospace and Electronic Systems ; Volume 36, Issue 3 PART 1 , 2000 , Pages 889-897 ; 00189251 (ISSN) Ali, M ; Mohammad, K ; Bastani, H ; Sharif University of Technology
    2000
    Abstract
    A new constant false alarm rate (CFAR) processor is presented, that exhibits a noticeable detection performance in the presence of interfering targets, as well as an excellent false alarm rate (FAR) regulation at the clutter power transition regions. The presented CFAR processor, which is designed to work on the logarithmic amplified video signals, can also easily adapt itself to new environmental conditions. Furthermore, in the steady state, its performance does not depend on the background noise power. Simulation results show the obvious preference of the presented processor to the conventional GOCA-LOG/CFAR, regarding FAR regulation at the clutter power transition regions. Noncoherent... 

    Investigation of core loss effect on steady-state characteristics of inverter fed brushless doubly fed machines

    , Article IEEE Transactions on Energy Conversion ; Volume 29, Issue 1 , March , 2014 , Pages 57-64 ; ISSN: 08858969 Hashemnia, M. N ; Tahami, F ; Oyarbide, E ; Sharif University of Technology
    Abstract
    Brushless doubly fed machine (BDFM) shows promising results for wind power and adjustable-speed drive applications. Due to poor rotor magnetic coupling and relatively high value of slip, core loss is an important factor which can affect the steady-state and dynamic performance of BDFM. Specifically, core loss plays a major role when evaluating the efficiency of the machine. By now, there is no comprehensive study on core loss effect on performance characteristics of BDFM in the literature. In this paper, based on the derived relations and applying transformation of parameters from one winding to another one, the steady-state equivalent circuit model of BDFM without core loss is modified in... 

    Numerical solution of homogeneous double pipe heat exchanger: Dynamic modeling

    , Article Scientia Iranica ; Volume 21, Issue 2 , 2014 , pp. 449-455 ; ISSN: 10263098 AliHosseinpour, H ; Kazemi, Y ; Fattahi, M ; Sharif University of Technology
    Abstract
    Dynamic modeling of a double-pipe heat exchanger is the subject of the current study. The basis of this study is the same velocity of vapor and liquid phases or, in other words, homogeneous phase, in the annulus part of the exchanger. The model can predict the temperature and vapor quality along the axial pipe from the pipe inlet up to a distance where steady state conditions are achieved. The simulation is conducted for two modes of co- and counter-flow in a one dimensional transient system. The physical properties of water are estimated from empirical correlation and a saturated vapor table with cubic spline interpolation. The exchanger model, which is a set of Ordinary Differential... 

    An analytical model for stress analysis of short fiber composites in power law creep matrix

    , Article International Journal of Non-Linear Mechanics ; Volume 57 , 2013 , Pages 39-49 ; 00207462 (ISSN) Mondali, M ; Abedian, A ; Sharif University of Technology
    2013
    Abstract
    The creep deformation behavior of short fiber composites has been studied by an approximate analytical model. A perfect fiber/matrix interfacial bond is assumed and a power law function is considered for describing the steady state creep behavior of the matrix material. The results obtained from the proposed analytical solution satisfy the equilibrium and constitutive creep equations. Also, a parametric study was undertaken to define the effects of geometric parameters on the steady state creep strain rate of short fiber composites. The present model is then validated using the results of finite element method. The predicted strain rate and stress components by the proposed analytical... 

    CDM-based closed-loop transfer function design for ramp input

    , Article Transactions of the Institute of Measurement and Control ; Volume 33, Issue 5 , 2011 , Pages 558-572 ; 01423312 (ISSN) Haeri, M ; Tavazoei, M. S ; Sharif University of Technology
    2011
    Abstract
    This paper presents a method to determine the denominator and numerator polynomials of a closed-loop transfer function in order to obtain desired transient and steady-state responses in terms of the overshoot, speed (time needed for the relative error to become less than a specific amount) and the steady-state error when the desired output is a ramp signal. Meanwhile, a controller is designed with the same characteristic equation for the closed-loop system to eliminate step and ramp disturbances  

    Study of nonlinear dynamics and chaos in MEMS/NEMS resonators

    , Article Communications in Nonlinear Science and Numerical Simulation ; Volume 22, Issue 1-3 , May , 2015 , Pages 611-622 ; 10075704 (ISSN) Miandoab, E. M ; Yousefi Koma, A ; Pishkenari, H. N ; Tajaddodianfar, F ; Sharif University of Technology
    Elsevier  2015
    Abstract
    With the successes in numerous applications from signal filtering to chemical and mass sensing, micro- and nano-electro-mechanical resonators continue to be one of the most widely studied topics of the micro-electro-mechanical systems community. Nonlinearities arising out of different sources such as mid-plane stretching and electrostatic force lead to a rich nonlinear dynamics in the time response of these systems which should be investigated for appropriate design and fabrication of them. Motivated by this need, present study is devoted to analyzing the nonlinear dynamics and chaotic behavior of nano resonators with electrostatic forces on both sides. Based on the potential function and... 

    A novel approach for the steady-state analysis of a three-phase self excited induction generator including series compensation

    , Article ISIEA 2010 - 2010 IEEE Symposium on Industrial Electronics and Applications, 3 October 2010 through 5 October 2010, Penang ; 2010 , Pages 371-375 ; 9781424476473 (ISBN) Hashemnia, M. N ; Kashiha, A ; Ansari, K ; Sharif University of Technology
    2010
    Abstract
    A new method to evaluate the steady state performance of a three-phase self excited induction generator based on conductance minimization is proposed. It can be simply used to take series compensation into account. Among the priorities of this method are the absence of convergence problem and flexibility. Simple methods to find the frequency and magnetizing reactance have been proposed. Simulation results show the efficiency of this method  

    A novel efficient model for the power flow analysis of power systems

    , Article Turkish Journal of Electrical Engineering and Computer Sciences ; Volume 23, Issue 1 , 2015 , Pages 52-66 ; 13000632 (ISSN) Safdarian, A ; Fotuhi Firuzabad, M ; Aminifar, F ; Sharif University of Technology
    Abstract
    The overall system status calculated by pflower flow analysis is the most basic information used for all decisions taken by power system operators and planners. While conventional AC pflower flow solutions are computationally tractable, approximate DC models are employed in many applications, such as optimal power flow studies and unit commitment problems, mainly due to the linear nature of DC models. These models do not provide any information on the reactive power and voltage magnitude quantities and occasionally inaccurate results of the active power values. This paper presents an efficient power flow approach compromising both the con icting aspects of speed and accuracy. The proposed... 

    A new algorithm to solve sinusoidal steady-state Maxwell's equations on unstructured grids

    , Article Scientia Iranica ; Volume 25, Issue 3B , 2018 , Pages 1296-1302 ; 10263098 (ISSN) Azimi, S ; Saidi, M. S ; Sharif University of Technology
    Sharif University of Technology  2018
    Abstract
    A new approach for attaining numerical solution to sinusoidal steady-state Maxwell's equations is developed. This approach is based on Yee's method, and can be applied on unstructured grids. A problem is solved by the method and the results show good agreement with the available analytical solution. This method can be improved to be applicable for general unsteady problems. © 2018 Sharif University of Technology. All rights reserved  

    Detection of change to SSVEPs using analysis of phase space topological : a novel approach

    , Article Neurophysiology ; Volume 51, Issue 3 , 2019 , Pages 180-190 ; 00902977 (ISSN) Soroush, M. Z ; Maghooli, K ; Pisheh, N. F ; Mohammadi, M ; Soroush, P. Z ; Tahvilian, P ; Sharif University of Technology
    Springer New York LLC  2019
    Abstract
    A novel method based on EEG nonlinear analysis and analysis of steady-state visual evoked potentials (SSVEPs) has been processed. The EEG phase space is reconstructed, and some new geometrical features are extracted. Statistical analysis is carried out based on ANOVA, and most significant features are selected and then fed into a multi-class support vector machine (MSVM). Both offline and online phases are considered to fully address SSVEP detection. In the offline mode, the whole design evaluation, feature selection, and classifier training are performed. In the online scenario, the proposed method is evaluated and the detection rate is reported for both phases. Subject-dependent and...