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Size-dependent interaction of an edge dislocation with an elliptical nano-inhomogeneity incorporating interface effects
, Article International Journal of Solids and Structures ; Volume 49, Issue 5 , March , 2012 , Pages 759-770 ; 00207683 (ISSN) ; Ahmadzadeh Bakhshayesh, H ; Gutkin, M. Y
2012
Abstract
The elastic behavior of an edge dislocation, which is positioned outside of a nanoscale elliptical inhomogeneity, is studied within the interface elasticity approach incorporating the elastic moduli and surface tension of the interface. The complex potential function method is used. The dislocation stress field and the image force acting on the dislocation are found and analyzed in detail. The difference between the solutions obtained within the classical-elasticity and interface-elasticity approaches is discussed. It is shown that for the stress field, this difference can be significant in those points of the inhomogeneity-matrix interface, where the radius of curvature is smaller and which...
Control of parallel three- phase inverters using optimal control and SVPWM technique
, Article IEEE International Symposium on Industrial Electronics, 5 July 2009 through 8 July 2009 ; 2009 , Pages 1823-1828 ; 9781424443499 (ISBN) ; Mokhtari, H ; Sharif University of Technology
2009
Abstract
In this paper, optimal control strategy is applied to parallel three-phase inverters using SVPWM technique. The three-phase system is transformed to a synchronous-stationary frame, suitable cost functions are defined, and the switching schemes are determined for the inverters. The control strategy minimizes the circulating current between the inverters, therefore, proper load sharing scheme is achieved. Simulations are performed for steady state and load change operation, and the results which show the suitability of the controller are provided. ©2009 IEEE
Identification of an aspidospermine derivative from borage extract as an anti-amyloid compound: A possible link between protein aggregation and antimalarial drugs
, Article Phytochemistry ; Volume 140 , 2017 , Pages 134-140 ; 00319422 (ISSN) ; Ashrafian, H ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
A number of human diseases, including Alzheimer's and Parkinson's have been linked to amyloid formation. To search for an anti-amyloidogenic product, alkaloid enriched extract from borage leaves was examined for anti-amyloidogenic activity using Hen Egg White Lysozyme (HEWL) as a model protein. After isolation of the plant extract using rHPLC, only one fraction indicated a significant bioactivity. TEM analysis confirmed a remarkable reduction of amyloid fibrils in the presence of the bioactive fraction. To identify the effective substance in the fraction, mass spectrometry, FTIR, and NMR were performed. Our analyses determined that the bioactive compound as...
Weakly nonlocal micromorphic elasticity for diamond structures vis-à-vis lattice dynamics
, Article Mechanics of Materials ; Volume 147 , 2020 ; Moosavian, H ; Sharif University of Technology
Elsevier B.V
2020
Abstract
In this work, after formulating the weakly nonlocal micromorphic equations of motion for non-Bravais crystals with general anisotropy, specialization to diamond structures is made. A critical dilemma is the determination of the elastic moduli tensor appearing in the equations of motion. From the equivalency of these equations with the pertinent equations obtained in the context of lattice dynamics, the expressions of the components of the elastic moduli tensors in terms of the atomic force constants are derived analytically. Subsequently, the atomic force constants are calculated via ab initio density functional perturbation theory (DFPT) with high precision. As a benchmark for the accuracy...
Nonlinear cylindrical bending analysis of shear deformable functionally graded plates under different loadings using analytical methods
, Article International Journal of Mechanical Sciences ; Volume 50, Issue 12 , 2008 , Pages 1650-1657 ; 00207403 (ISSN) ; Haddadpour, H ; Sharif University of Technology
2008
Abstract
An exact solution is presented for the nonlinear cylindrical bending and postbuckling of shear deformable functionally graded plates in this paper. A simple power law function and the Mori-Tanaka scheme are used to model the through-the-thickness continuous gradual variation of the material properties. The von Karman nonlinear strains are used and then the nonlinear equilibrium equations and the relevant boundary conditions are obtained using Hamilton's principle. The Navier equations are reduced to a linear ordinary differential equation for transverse deflection with nonlinear boundary conditions, which can be solved by exact methods. Finally, by solving some numeral examples for simply...
Aero-thermoelastic stability of functionally graded plates
, Article Composite Structures ; Volume 80, Issue 4 , 2007 , Pages 580-587 ; 02638223 (ISSN) ; Haddadpour, H ; Sharif University of Technology
2007
Abstract
In this paper, an analytical investigation intended to determine the aero-thermoelastic stability margins of functionally graded panels is carried out. For this purpose, piston theory aerodynamics has been employed to model quasi-steady aerodynamic loading. The material properties of the plate are assumed to be graded continuously across the panel thickness. A simple power-law and the Mori-Tanaka scheme are used for estimating the effective material properties such as temperature-dependent thermoelastic properties. The effects of compressive in-plane loads and both uniform and through the thickness non-linear temperature distributions are also considered. Hamilton's principle is used to...
Application of Dwell time functions in transit assignment model
, Article Transportation Research Record ; Issue 1817 , 2002 , Pages 88-92 ; 03611981 (ISSN) ; Iravani, H ; Sharif University of Technology
National Research Council
2002
Abstract
The transit assignment process applied as part of the development of the Tehran transportation model is described. The process includes development of various models Tor dwell time as a function of transit volume. Dwell time is the time a transit vehicle spends at a stop to allow passengers to alight and board. This method was implemented by using EMME/2 transportation planning software. The calculation of dwell time is necessary in modeling transit assignment because an accurate estimation of dwell time will lead to more precise transit assignment results. The area analyzed in the model comprises various transportation analysis zones in the city of Tehran. The model output was shown to be...
Braess' phenomenon in the management of networks and dissociation of equilibrium concepts
, Article Transportation Planning and Technology ; Volume 27, Issue 6 , 2004 , Pages 469-482 ; 03081060 (ISSN) ; Poorzahedy, H ; Sharif University of Technology
2004
Abstract
Braess' phenomenon, also known as Braess' paradox, is a phenomenon that has received considerable attention in transportation engineering and planning, as well as in other fields. It has an important implication in the area of investment in transportation networks, namely that adding a new link in a network may increase the cost to the users of that network. In this paper we show this phenomenon in a new environment. Unlike traditional examples, which involve the physical addition of a link to a network (a 0/1 integer decision variable), an example is presented where the decision variable is continuous in nature. Moreover, this example conveys two new messages. First, it is shown that some...
Nanocrystallization kinetics and magnetic properties of the melt spun amorphous (Fe0.5Co0.5)77Si11B 9Cu0.6Nb2.4 alloy
, Article Thermochimica Acta ; Vol. 575, issue , 2014 , p. 64-69 ; Samadi, M ; Alihosseini, H ; Madaah Hosseini, H. R ; Sharif University of Technology
2014
Abstract
Kinetics of crystallization in an amorphous (Fe0.5Co 0.5)77Si11B9Cu0.6Nb 2.4 (at.%) alloy was investigated using differential scanning calorimetry (DSC). Transformed fraction as a function of temperature was obtained by accurate DSC measurement and the experimental data analyzed with Vyazovkin model-free kinetic method. Reconstructed form of the experimental kinetics model, g(α), clearly showed the crystallization mechanism do not belongs to a single model but almost follows the Avrami-Erofe'ev. Magnetic coercivity and hysteresis loss values of the annealed samples at 823 K were 7.5 A m-1 and 1.2 J m-3, compared to 17.1 A m-1 and 37.1 J m-3 for as spun samples. Magnetic measurements show the...
On the reduction of the number of required motions in the dynamic analysis using a refined spectral matching
, Article Earthquake and Structures ; Volume 21, Issue 4 , 2021 , Pages 425-444 ; 20927614 (ISSN) ; Mashayekhi, M ; Mohammadnezhad, H ; Jaberi, H ; Estekanchi, H. E ; Sharif University of Technology
Techno-Press
2021
Abstract
This study aims to show the efficiency of a proposed spectral matching technique for the reduction of required ground motions in the dynamic time history analysis. In this non-stationary spectral matching approach, unconstrained optimization is employed to adjust the signal to match a target spectrum. Adjustment factors of discrete wavelet transform (DWT) coefficients associated with the signals are then considered as decision variables and the Levenberg-Marquardt algorithm is employed to find the optimum values of DWT coefficients. This matching algorithm turns out to be quite effective in the spectral matching objective, where matching at multiple damping ratios can be readily achieved....
Optimal MIMO waveform design with controlled characteristics
, Article Proceedings International Radar Symposium, 24 June 2015 through 26 June 2015 ; Volume 2015-August , 2015 , Pages 1141-1146 ; 21555753 (ISSN) ; 9783954048533 (ISBN); 9783954048533 (ISBN); 9783954048533 (ISBN) ; Radmard, M ; Nayebi, M. M ; Bastani, M. H ; Rohling, H ; Rohling, H ; Rohling, H ; Sharif University of Technology
IEEE Computer Society
2015
Abstract
In a MIMO (Multiple Input Multiple Output) radar system, proper design of transmit signal and receive filter is an advantageous tool to improve the detection performance. Thus, in this paper, we consider the problem of transmit code and receive filter design, in order to maximize the Signal to Noise Ratio (SNR) at the receiver while enforcing a similarity constraint between the transmit space-time code (STC) and a reference STC which has a desirable ambiguity function. We will show that by solving such constrained optimization problem through successive iterations, our proposed method leads to satisfactory results
Incorporating betweenness centrality in compressive sensing for congestion detection
, Article ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings ; 2013 , Pages 4519-4523 ; 15206149 (ISSN); 9781479903566 (ISBN) ; Rabiee, H. R ; Rohban, M. H ; Salehi, M ; Sharif University of Technology
2013
Abstract
This paper presents a new Compressive Sensing (CS) scheme for detecting network congested links. We focus on decreasing the required number of measurements to detect all congested links in the context of network tomography. We have expanded the LASSO objective function by adding a new term corresponding to the prior knowledge based on the relationship between the congested links and the corresponding link Betweenness Centrality (BC). The accuracy of the proposed model is verified by simulations on two real datasets. The results demonstrate that our model outperformed the state-of-the-art CS based method with significant improvements in terms of F-Score
Investigation of microstructure effect on fretting fatigue crack initiation using crystal plasticity
, Article Fatigue and Fracture of Engineering Materials and Structures ; 2018 ; 8756758X (ISSN) ; Farrahi, G. H ; Karimpour, M ; Bahai, H ; Majzoobi, G. H ; Sharif University of Technology
Blackwell Publishing Ltd
2018
Abstract
The onset of fretting fatigue is characterized by material microstructural changes in which the extent of the damage is comparable to grain size, and hence, the microstructure characteristics could have a significant effect on fatigue crack initiation. In this paper, a three-dimensional finite element crystal plasticity framework is presented for simulation of the fretting fatigue. Controlled Poisson Voronoi tessellation (CPVT) method is employed to generate the polycrystalline region. In the CPVT method, regularity parameter controls the shape of grains. In this study, the impact of grain size and regularity parameter on crack initiation life and initiation site has been investigated....
Investigation of microstructure effect on fretting fatigue crack initiation using crystal plasticity
, Article Fatigue and Fracture of Engineering Materials and Structures ; Volume 42, Issue 3 , 2019 , Pages 640-650 ; 8756758X (ISSN) ; Farrahi, G. H ; Karimpour, M ; Bahai, H ; Majzoobi, G. H ; Sharif University of Technology
Blackwell Publishing Ltd
2019
Abstract
The onset of fretting fatigue is characterized by material microstructural changes in which the extent of the damage is comparable to grain size, and hence, the microstructure characteristics could have a significant effect on fatigue crack initiation. In this paper, a three-dimensional finite element crystal plasticity framework is presented for simulation of the fretting fatigue. Controlled Poisson Voronoi tessellation (CPVT) method is employed to generate the polycrystalline region. In the CPVT method, regularity parameter controls the shape of grains. In this study, the impact of grain size and regularity parameter on crack initiation life and initiation site has been investigated....
Analysis of large amplitude free vibrations of clamped tapered beams on a nonlinear elastic foundation
, Article Applied Mathematical Modelling ; Volume 38, Issue 3 , 1 February , 2014 , Pages 1176-1186 ; ISSN: 0307904X ; Mazaheri, H ; Salarieh, H ; Sharif University of Technology
2014
Abstract
The purpose of this paper is to present efficient and accurate analytical expressions for large amplitude free vibration analysis of single and double tapered beams on elastic foundation. Geometric nonlinearity is considered using the condition of inextensibility of neutral axis. Moreover, the elastic foundation consists of a linear and cubic nonlinear parts together with a shearing layer. The nonlinear governing equation is solved by employing the variational iteration method (VIM). This study shows that the second-order approximation of the VIM leads to highly accurate solutions which are valid for a wide range of vibration amplitudes. The effects of different parameters on the nonlinear...
Dynamic instability of cantilevered composite pipe conveying flow with an end nozzle
, Article 21st International Congress on Sound and Vibration 2014, ICSV 2014 ; Vol. 4, issue , 13- 17 July , 2014 , pp. 3564-3571 ; ISBN: 9781634392389 ; Abtahi, H ; Haddadpour, H ; Sharif University of Technology
2014
Abstract
In this paper, the instability of cantilevered horizontal composite pipes is investigated. To this aim, the lateral flow forces are modelled as a distributed lateral force and the nozzle effect is modelled as a compressive axial follower force and a concentrated end mass. The coupled bending-torsional equations of motion are derived using Hamilton's principal and Galerkin method. In order to obtain the stability margin of the pipe, the standard Eigen value problem is solved. Finally, effects of elastic coupling parameter and nozzle aspect ratio are considered on the stability margin of the pipe and some conclusions are drawn
A new genetic algorithm for multiple sequence alignment
, Article International Journal of Computational Intelligence and Applications ; Volume 11, Issue 4 , December , 2012 ; 14690268 (ISSN) ; Beigy, H ; Abolhassani, H ; Sharif University of Technology
2012
Abstract
Multiple sequence alignment (MSA) is one of the basic and important problems in molecular biology. MSA can be used for different purposes including finding the conserved motifs and structurally important regions in protein sequences and determine evolutionary distance between sequences. Aligning several sequences cannot be done in polynomial time and therefore heuristic methods such as genetic algorithms can be used to find approximate solutions of MSA problems. Several algorithms based on genetic algorithms have been developed for this problem in recent years. Most of these algorithms use very complicated, problem specific and time consuming mutation operators. In this paper, we propose a...
A decentralized self-adjusting control strategy for reactive power management in an islanded multi-bus MV microgrid
, Article Canadian Journal of Electrical and Computer Engineering ; Volume 36, Issue 1 , 2013 , Pages 18-25 ; 08408688 (ISSN) ; Mokhtari, H ; Karimi, H ; Sharif University of Technology
2013
Abstract
This paper presents a decentralized self-adjusting reactive power controller for the autonomous operation of a multi-bus medium voltage (MV) microgrid. The main objective of the proposed control strategy of each distributed generation (DG) unit is to compensate the reactive power of its local loads and to share the reactive power of the nonlocal loads among itself and other DG units. The proposed control strategy includes an improved droop controller whose parameters are adjusted according to the reactive power of the local loads. A virtual inductive impedance loop is augmented to the voltage controller to enhance the steady state and transient responses of the proposed reactive power...
An optimal time algorithm for minimum linear arrangement of chord graphs
, Article Information Sciences ; Volume 238 , 2013 , Pages 212-220 ; 00200255 (ISSN) ; Rostami, H ; Bagherinezhad, H ; Sharif University of Technology
2013
Abstract
A linear arrangement φ of an undirected graph G = (V, E) with |V| = n nodes is a bijective function φ:V → {0, ..., n - 1}. The cost function is cost(G,φ)=∑uv∈E|(φ(u)-φ(v))| and opt(G) = min∀φcost(G, φ). The problem of finding opt(G) is called minimum linear arrangement (MINLA). The Minimum Linear Arrangement is an NP-hard problem in general. But there are some classes of graphs optimally solvable in polynomial time. In this paper, we show that the label of each node equals to the reverse of binary representation of its id in the optimal arrangement. Then, we design an O(n) algorithm to solve the minimum linear arrangement problem of Chord graphs
A new method of mining data streams using harmony search
, Article Journal of Intelligent Information Systems ; Volume 39, Issue 2 , 2012 , Pages 491-511 ; 09259902 (ISSN) ; Abolhassani, H ; Beigy, H ; Sharif University of Technology
Springer
2012
Abstract
Incremental learning has been used extensively for data stream classification. Most attention on the data stream classification paid on non-evolutionary methods. In this paper, we introduce new incremental learning algorithms based on harmony search. We first propose a new classification algorithm for the classification of batch data called harmony-based classifier and then give its incremental version for classification of data streams called incremental harmony-based classif ier. Finally, we improve it to reduce its computational overhead in absence of drifts and increase its robustness in presence of noise. This improved version is called improved incremental harmony-based classifier. The...