Search for: computational-methods
0.009 seconds
Total 127 records

    Nonexistence of limit cycles in two classes of predator-prey systems

    , Article Applied Mathematics and Computation ; Volume 175, Issue 1 , 2006 , Pages 356-365 ; 00963003 (ISSN) Aghajani, A ; Moradifam, A ; Sharif University of Technology
    This paper deals with the question of nonexistence of limit cycles in two famous classes of predator-prey systems. We present some sufficient conditions for the nonexistence of limit cycles in these systems. Our results extend and improve the results presented by Moghadas. © 2005 Elsevier Inc. All rights reserved  

    Improving forward solution for 2d block electrical impedance tomography using modified equations

    , Article Scientific Research and Essays ; Volume 5, Issue 11 , 2010 , Pages 1260-1263 ; 19922248 (ISSN) Abbasi, A ; Vahdat, B. V ; Sharif University of Technology
    Electrical impedance tomography is a simple and economic medical imaging technology which permits regional assessment of the electrical properties of organs within the body based on measurements made from electrodes on the surface of the body. Block method is a new solution for electrical impedance tomography used to enhance image resolution and to improve reconstruction algorithm. Image reconstruction by block method is an ill-posed and nonlinear problem also has memory and time consuming process which can be improved by using modified equations. Improving forward solution for block electrical impedance tomography method can make linear equations for image reconstruction algorithm  

    Solving the resource availability cost problem in project scheduling by path relinking and genetic algorithm

    , Article Applied Mathematics and Computation ; Volume 196, Issue 2 , 2008 , Pages 879-888 ; 00963003 (ISSN) Ranjbar, M ; Kianfar, F ; Shadrokh, S ; Sharif University of Technology
    This paper considers a project scheduling problem with the objective of minimizing resource availability costs required to execute the activities in a project by a given project deadline. The project contains activities interrelated by finish-start-type precedence relations with a time lag of zero, which require a set of renewable resources. Two metaheuristics, path relinking and genetic algorithm, are developed to tackle this problem in which a schedule is created with a precedence feasible priority list given to the schedule generation scheme. In these procedures, each new generation of solutions are created using the combination of current solutions. Comparative computational results... 

    An enhanced random-walk method for content locating in P2P networks

    , Article 27th International Conference on Distributed Computing Systems Workshops, ICDCSW'07, Toronto, ON, 22 June 2007 through 29 June 2007 ; 2007 ; 0769528384 (ISBN); 9780769528380 (ISBN) Ronasi, K ; Firooz, M. H ; Pakravan, M. R ; Nasiri Avanaki, A ; Sharif University of Technology
    The important problem of content location in an unstructured distributed network (such as P2P, with no central searching system, graph construction control or file placement regulation) is addressed. The existing methods that are based on either flooding or random walk impose a large traffic load on the network or require a long time to search. In this work, we propose a method that outperforms the existing methods in both of these measures. These advantages are achieved by publishing traces of the contents of each node in its nearby nodes, so that the closer nodes to the target have a stronger trace of it. Such traces are used to rapidly locate the desired content. The superb performance of... 

    A methodology for analyzing the transient availability and survivability of a system with repairable components

    , Article Applied Mathematics and Computation ; Volume 184, Issue 2 , 2007 , Pages 300-307 ; 00963003 (ISSN) Amiri, M ; Ghassemi Tari, F ; Sharif University of Technology
    In this paper we present a method for transient analysis of availability and survivability of a system with the identical components and identical repairmen. The considered system is supposed to consist of series of k-out-of-n or parallel components. We employed the Markov models, eigen vectors and eigenvalues for analyzing the transient availability and survivability of the system. The method is implemented through an algorithm which is tested in MATLAB programming environment. The new method enjoys a stronger mathematical foundation and more flexibility for analyzing the transient availability and survivability of the system. © 2006 Elsevier Inc. All rights reserved  

    High accurate multiple target detection in PCL radar systems

    , Article 2006 CIE International Conference on Radar, ICR 2006, Shanghai, 16 October 2006 through 19 October 2006 ; 2006 ; 0780395824 (ISBN); 9780780395824 (ISBN) Jafargholi, A ; Mousavi, M. R ; Nayebi, M. M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2006
    A new approach in multiple target detection in PCL (Passive Coherent Location) radars based on TV and Radio ambiguity function processing is presented. Fast computation and high Accuracy are the presented algorithm capabilities. Presented algorithm is a new and simple method which could provide perfect detection in noisy environment up to SNR= -30 dB  

    A categorization scheme for semantic web search engines

    , Article IEEE International Conference on Computer Systems and Applications, 2006, Sharjah, 8 March 2006 through 8 March 2006 ; Volume 2006 , 2006 , Pages 171-178 ; 1424402123 (ISBN); 9781424402120 (ISBN) Sheykh Esmaili, K ; Abolhassani, H ; Sharif University of Technology
    IEEE Computer Society  2006
    Semantic web search engines are evolving and many prototype systems and some implementation have been developed. However, there are some different views on what a semantic search engine should do. In this paper, a categorization scheme for semantic web search engines are introduced and elaborated. For each category, its components are described according to a proposed general architecture and various approaches employed in these components are discussed. We also propose some factors to evaluate systems in each category. © 2006 IEEE  

    Comparison between different synchronization methods of identical chaotic systems

    , Article Chaos, Solitons and Fractals ; Volume 29, Issue 4 , 2006 , Pages 1002-1022 ; 09600779 (ISSN) Haeri, M ; Khademian, B ; Sharif University of Technology
    This paper studies and compares three nonadaptive (bidirectional, unidirectional, and sliding mode) and two adaptive (active control and backstepping) synchronization methods on the synchronizing of four pairs of identical chaotic systems (Chua's circuit, Rössler system, Lorenz system, and Lü system). Results from computer simulations are presented in order to illustrate the effectiveness of the methods and to compare them based on different criteria. © 2005 Elsevier Ltd. All rights reserved  

    A recursive approach for analysis of snake robots using Kane's equations

    , Article DETC2005: ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, Long Beach, CA, 24 September 2005 through 28 September 2005 ; Volume 7 B , 2005 , Pages 855-861 ; 0791847446 (ISBN) Tavakoli Nia, H ; Pishkenari, H. N ; Meghdari, A ; Sharif University of Technology
    This paper presents a recursive approach for solving kinematic and dynamic problem in snake-like robots using Kane's equations. An n-link model with n-nonholonomic constraints is used as the snake robot model in our analysis. The proposed algorithm which is used to derive kinematic and dynamic equations recursively enhances the computational efficiency of our analysis. Using this method we can determine the number of additions and multiplications as a function of n. The proposed method is compared with the Lagrange and Newton-Euler's method in three different aspects: Number of operations, CPU time and error in the computational procedures. Copyright © 2005 by ASME  

    SHRAD: A language for sequential real number computation

    , Article First Conference on Computability in Europe, CiE 2005: New Computational Paradigms, Amsterdam, 8 June 2005 through 12 June 2005 ; Volume 3526 , 2005 , Pages 128- ; 03029743 (ISSN) Farjudian, A ; Sharif University of Technology
    Springer Verlag  2005
    Since Di Gianantonio introduced his semantics for exact real number computation, there has always been a struggle to maintain data abstraction and efficiency as much as possible. The interval domain model - or its variations - can be regarded as the standard setting to obtain maximum data abstraction. As for efficiency there has been much focus on sequentially to the extent that these two terms have become almost synonymous. [2, 3] demonstrated that there is not much one can get by sequential computation in the interval domain model. In [4, 5] we reinforced this result by exposing the limited power of (some extensions of) the sequential fragment of Real-PCF. The previous argument suggests... 

    Parallel computation of a mixed convection problem using fully-coupled and segregated algorithms

    , Article 2004 ASME International Mechanical Engineering Congress and Exposition, IMECE, Anaheim, CA, 13 November 2004 through 19 November 2004 ; Volume 375, Issue 1 , 2004 , Pages 313-322 ; 02725673 (ISSN) Darbandi, M ; Banaeizadeh, A ; Schneider, G. E ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2004
    In this work, parallel solution of the Navier-Stokes equations for a mixed convection heat problem is achieved using a finite-element-based finite-volume method in fully coupled and semi coupled algorithms. A major drawback with the implicit methods is the need for solving the huge set of linear algebraic equations in large scale problems. The current parallel computation is developed on distributed memory machines. The matrix decomposition and solution are carried out using PETSc library. In the fully coupled algorithm, there is a 36-diagonal global matrix for the two-dimensional governing equations. In order to reduce the computational time, the matrix is suitably broken in several... 

    A Model for Analysis of Computational Learning

    , M.Sc. Thesis Sharif University of Technology Sattari Javid, Ali (Author) ; Daneshgar, Amir (Supervisor)
    The subject of this thesis is about a certain set of algorithms that try to indirectly solve problems. Instead of a programmer crafting an algorithm to solve a problem, these algorithms learn a solution themselves. These methods are usually studied in the Probably Accurately Correct (PAC) learning model. Although, PAC Learning is a generally accepted model, it falls short to describe certain aspects of learning algorithms. Many learning methods rely on convergence to minimize error, or maximize their fitness, yet the PAC model doesn’t explicitly provide any means to measure these behaviours. In this thesis, we first go through different models related to computational requirements of... 

    Protein Function Prediction Using Protein Structure and Computational Methods

    , M.Sc. Thesis Sharif University of Technology Abbasi Dezfouli, Mohammad Ebrahim (Author) ; Fatemizadeh, Emad (Supervisor) ; Arab, Shahriar ($item.subfieldsMap.e)
    Predicting the Amino Acids that have a catalytic effect in the enzymes, is a big step in appointing the activity of the enzymes and classifying them. This is a very challenging job, because an Amino Acid can appear in a variety of active sites.The biological activity of a protein usually depends on the existence of a small number of Amino Acids. Detecting these Amino Acids from the sequence of Amino Acids has many applications. Usually, the Amino Acids that are preserved are known as the Amino Acids that build up the active site, but the algorithms for finding the preserved Amino Acids are much more complex. There are a lot of algorithms for predicting the active sites of Amino Acids, but... 

    Color PCA eigenimages and their application to compression and watermarking

    , Article Image and Vision Computing ; Volume 26, Issue 7 , 2008 , Pages 878-890 ; 02628856 (ISSN) Abadpour, A ; Kasaei, S ; Sharif University of Technology
    Elsevier Ltd  2008
    From the birth of multi-spectral imaging techniques, there has been a tendency to consider and process this new type of data as a set of parallel gray-scale images, instead of an ensemble of an n-D realization. However, it has been proved that using vector-based tools leads to a more appropriate understanding of color images and thus more efficient algorithms for processing them. Such tools are able to take into consideration the high correlation of the color components and thus to successfully carry out energy compaction. In this paper, a novel method is proposed to utilize the principal component analysis in the neighborhoods of an image in order to extract the corresponding eigenimages.... 

    Penetration-elimination method for five-axis CNC machining of sculptured surfaces

    , Article International Journal of Machine Tools and Manufacture ; Volume 47, Issue 10 , 2007 , Pages 1625-1635 ; 08906955 (ISSN) Hosseinkhani, Y ; Akbari, J ; Vafaeesefat, A ; Sharif University of Technology
    In this paper, a new tool positioning strategy for five-axis machining, called the penetration-elimination method (PEM), is introduced. The PEM gains from two innovative techniques that can considerably improve the computational efficiency during the calculation of the optimal tool orientations. The first technique includes developing a quantitative definition for the gouging concept and using this definition in conjunction with powerful numerical root-finder algorithms to determine the optimized tool orientations. The second technique dynamically detects the ineffective grid points and drops them from calculations and consequently takes a great role in reducing the computational burden. The... 

    Extended reduced rank two Abaffian update schemes in the ABS-type methods

    , Article Applied Mathematics and Computation ; Volume 185, Issue 1 , 2007 , Pages 255-265 ; 00963003 (ISSN) Amini, K ; Mahdavi Amiri, N ; Peyghami, M. R ; Sharif University of Technology
    The ABS methods, introduced by Abaffy, Broyden and Spedicato, are direct iteration methods for solving a linear system where the ith iterate satisfies the first i equations, therefore a system of m equations is solved in at most m steps. Recently, we have presented a new approach to devise a class of ABS-type methods for solving full row rank systems [K. Amini, N. Mahdavi-Amiri, M. R. Peyghami, ABS-type methods for solving full row rank linear systems using a new rank two update, Bulletin of the Australian Mathematical Society 69 (2004) 17-31], the ith iterate of which solves the first 2i equations. Here, to reduce the space and computation time, we use a new extended rank two update formula... 

    A computational thermodynamics approach to the Gibbs-Thomson effect

    , Article Materials Science and Engineering A ; Volume 443, Issue 1-2 , 2007 , Pages 178-184 ; 09215093 (ISSN) Shahandeh, S ; Nategh, S ; Sharif University of Technology
    In two-phase system, curvature of interface leads to increase of solute concentration in matrix. This effect plays a significant role in solidification, precipitation, nucleation and growth and coarsening. There are number of models and formulas for Gibbs-Thomson effect in binary alloys. In this paper with the help of CALPHAD calculations, new approach for describing this effect in binary and multicomponent systems is proposed. In this generalized method no traditional simplifying assumption are considered and this yield to more accurate result for Gibbs-Thomson phenomenon. This model is compared with previous formulas in some case alloying systems. © 2006 Elsevier B.V. All rights reserved  

    On pancyclicity properties of OTIS networks

    , Article 3rd International Conference on High Performance Computing and Communications, HPCC 2007, Houston, TX, 26 September 2007 through 28 September 2007 ; Volume 4782 LNCS , 2007 , Pages 545-553 ; 03029743 (ISSN); 9783540754435 (ISBN) Hoseinyfarahabady, M. R ; Sarbazi Azad, H ; Sharif University of Technology
    Springer Verlag  2007
    The OTIS-Network (also referred to as two-level swapped network) is composed of n clones of an n-node original network constituting its clusters. It has received much attention due to its many favorable properties such as high degree of scalability, regularity, modularity, package-ability and high degree of algorithmic efficiency. In this paper, using the construction method, we show that the OTIS-Network is Pancyclic if its basic network is Hamiltonian- connected. The study of cycle embeddings with different sizes arises naturally in the implementation of a number of either computational or graph problems such as those used for finding storage schemes for logical data structures, layout of... 

    Estimating the mixing matrix in sparse component analysis based on converting a multiple dominant to a single dominant problem

    , Article 7th International Conference on Independent Component Analysis (ICA) and Source Separation, ICA 2007, London, 9 September 2007 through 12 September 2007 ; Volume 4666 LNCS , 2007 , Pages 397-405 ; 03029743 (ISSN); 9783540744931 (ISBN) Noorshams, N ; Babaie Zadeh, M ; Jutten, C ; Sharif University of Technology
    Springer Verlag  2007
    We propose a new method for estimating the mixing matrix, A, in the linear model x(t) = As(t),t = 1,...,T, for the problem of underdetermined Sparse Component Analysis (SCA). Contrary to most previous algorithms, there can be more than one dominant source at each instant (we call it a "multiple dominant" problem). The main idea is to convert the multiple dominant problem to a series of single dominant problems, which may be solved by well-known methods. Each of these single dominant problems results in the determination of some columns of A. This results in a huge decrease in computations, which lets us to solve higher dimension problems that were not possible before. © Springer-Verlag... 

    A numerical study of swage autofrettage of thick-walled tubes

    , Article Materials and Design ; Volume 28, Issue 3 , 2007 , Pages 804-815 ; 02613069 (ISSN) Bihamta, R ; Movahhedy, M. R ; Mashreghi, A. R ; Sharif University of Technology
    Elsevier Ltd  2007
    Swage autofrettage process is used for internal forming and sizing of thick-walled tubes designed to withstand high internal pressures. In this process, a mandrel with a diameter slightly larger than that of the tube is pressed inside the tube and in so doing, creates the internal profile. This paper presents an experimental and numerical study of this process. Two dimensional axi-symmetric and three dimensional finite element analyses are used to investigate the effects of workpiece and mandrel geometry on the forming load and part quality. Experiments are carried out to validate the numerical results. © 2005 Elsevier Ltd. All rights reserved