Loading...
Search for: feedback
0.011 seconds
Total 433 records

    The dynamics of gain-coupled distributed feedback dye laser: Feedback mechanism and laser field evolution

    , Article Laser Physics ; Volume 28, Issue 9 , 2018 ; 1054660X (ISSN) Pasandideh, K ; Alijabbari, M ; Gohari Kamel, N ; Golshani, M ; Sadighi Bonabi, R ; Sharif University of Technology
    Institute of Physics Publishing  2018
    Abstract
    The temporal and spatial evolution of the two counter-propagating laser waves inside the active medium of a gain coupled distributed feedback dye laser is studied via a dynamic model. More specifically, the feedback mechanism, the temporal and spatial evolution of laser waves, the interaction between them, and the effect of pump pulse characteristics on the feedback strength are explained. It is shown that a pumping configuration with a spatial Gaussian pattern strongly decreases the laser pulse energy. This has never proposed or described by other models in the literature. For a narrow Gaussian pump pulse, the distributed feedback lasing on both sides of the active medium vanishes and... 

    Observer based feedback control of a biodynamical model of tumor growth with sampled measurements

    , Article 2016 European Control Conference, ECC 2016, 29 June 2016 through 1 July 2016 ; 2017 , Pages 2423-2428 ; 9781509025916 (ISBN) Gholami, S ; Salarieh, H ; Alasty, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    Abstract
    This paper deals with the cancer treatment scheduling via observer-based feedback control of a tumor growth biodynamical model. An experimental nonlinear model is utilized to design a feedback controller. This model was validated by a pharmacological study on xenograft models obtained by transplantation of colon carcinoma cell lines in athymic mice. Input-output feedback linearization approach is used to linearize the nonlinear model of the system and design a control law. It is assumed that tumor weight can be measured in definite intervals. So a continuous-discrete observer is designed to estimate states of the system based on discrete sampled data which are tumor weight in this case. To... 

    Delayed feedback control of chaotic spinning disk via minimum entropy approach

    , Article Nonlinear Analysis, Theory, Methods and Applications ; Volume 69, Issue 10 , 2008 , Pages 3273-3280 ; 0362546X (ISSN) Salarieh, H ; Alasty, A ; Sharif University of Technology
    2008
    Abstract
    Chaos control of a spinning disk model via delayed feedback method is presented. The feedback gain is obtained and adapted according to a minimum entropy (ME) algorithm. In this method, stabilizing an unstable fixed point of the system Poincare map is achieved by minimizing the entropy of point distribution on the Poincare section. Simulation results show the feasibility of the proposed method in applying the delayed feedback technique for chaos control of spinning disks. © 2007 Elsevier Ltd. All rights reserved  

    A feature relevance estimation method for content-based image retrieval

    , Article International Journal of Information Technology and Decision Making ; Volume 10, Issue 5 , 2011 , Pages 933-961 ; 02196220 (ISSN) Ajorloo, H ; Lakdashti, A ; Sharif University of Technology
    Abstract
    Feature relevance estimation is one of the most successful techniques used for improving the retrieval results of a content-based image retrieval (CBIR) system based on users' feedbacks. In this class of approaches, the weights of the feature elements (FEs) are adjusted based on the relevance feedbacks (RFs) given by the users to reduce the so-called semantic gap in the underlying CBIR system. An analytical approach is proposed in this paper to convert the users' feedbacks to the appropriate FE weights by solving a constrained optimization problem. Experiments on a set of 11,000 images from the Corel database show that the proposed approach outperforms other existing short-term RF approaches... 

    Implementing an automated feedback program for a foreign language writing course: A learner-centric study

    , Article Journal of Computer Assisted Learning ; Volume 37, Issue 5 , 2021 , Pages 1494-1507 ; 02664909 (ISSN) Hassanzadeh, M ; Fotoohnejad, S ; Sharif University of Technology
    John Wiley and Sons Inc  2021
    Abstract
    Considering the prominence attached to written corrective feedback (WCF) within the domain of second/foreign language (L2) acquisition, automated writing evaluation (AWE) tools have steadily gained ground over the last two decades. The current study was an attempt to investigate the extent incorporating an AWE program, known as Criterion®, within a process writing framework would affect learners' writing quality in an English as a foreign language context. Moreover, we drew a comparison between the overall effects of computer- versus teacher-generated WCF. Participants consisted of 53 tertiary level students from two intact essay-writing classes. The within-group findings revealed that the... 

    FeedbackTrust: Using feedback effects in trust-based recommendation systems

    , Article 3rd ACM Conference on Recommender Systems, RecSys'09, New York, NY, 23 October 2009 through 25 October 2009 ; 2009 , Pages 269-272 ; 9781605584355 (ISBN) Moghaddam, S ; Jamali, M ; Ester, M ; Habibi, J ; Sharif University of Technology
    Abstract
    With the advent of online social networks, the trust-based approach to recommendation has emerged which exploits the trust network among users and makes recommendations based on the ratings of trusted users in the network. In this paper, we introduce a two dimensional trust model which dynamically gets updated based on users's feedbacks, in contrast to static trust values in current trust models. Explorability measures the extent to which a user can rely on recommendations returned by the social network of a trusted user. Dependability represents the extent to which a user's own ratings can be trusted by users trusting him directly and indirectly. We propose a method to learn the values of... 

    On the control of chaos via fractional delayed feedback method

    , Article Computers and Mathematics with Applications ; Vol. 62, Issue 3 , 2011 , pp. 1482-1491 ; ISSN: 8981221 Sadeghian, H ; Salarieh, H ; Alasty, A ; Meghdari, A ; Sharif University of Technology
    Abstract
    In this paper the problem of controlling unstable fixed points (in discrete systems) and periodic orbits (in continuous system) is investigated via a new scheme involving fractional derivatives. This method is based on applying feedback of measured states and using the period of fixed points and periodic orbits. In this method there is no need of information for fixed point and periodic orbits, just the period is enough. The effectiveness of this method is investigated via some demonstrative example  

    Output feedback control of satellite attitude using a single vector measurement

    , Article Proceedings of the IEEE Conference on Decision and Control, 10 December 2012 through 13 December 2012, Maui, HI ; 2012 , Pages 490-495 ; 01912216 (ISSN) Safaei, F ; Namvar, M ; Sharif University of Technology
    2012
    Abstract
    The existing methods in attitude control of satellites are based on employing the estimate of satellite attitude which is usually generated by using multiple vector measurements. In this paper we propose an output feedback control law that directly uses a single vector measurement and gyro, and without any need for estimating the satellite attitude. The output feedback gain is computed by solving a generalized Riccati time varying differential equation. We assume the moment-of-inertia matrix of satellite is unknown. The controller guarantees asymptotic convergence of the attitude to its desired value. A realistic simulation is presented where a magnetometer is used to provide the single... 

    On the control of chaos via fractional delayed feedback method

    , Article Computers and Mathematics with Applications ; Volume 62, Issue 3 , 2011 , Pages 1482-1491 ; 08981221 (ISSN) Sadeghian, H ; Salarieh, H ; Alasty, A ; Meghdari, A ; Sharif University of Technology
    Abstract
    In this paper the problem of controlling unstable fixed points (in discrete systems) and periodic orbits (in continuous system) is investigated via a new scheme involving fractional derivatives. This method is based on applying feedback of measured states and using the period of fixed points and periodic orbits. In this method there is no need of information for fixed point and periodic orbits, just the period is enough. The effectiveness of this method is investigated via some demonstrative example  

    Chaos control in uncertain dynamical systems using nonlinear delayed feedback

    , Article Chaos, Solitons and Fractals ; Volume 41, Issue 1 , 2009 , Pages 67-71 ; 09600779 (ISSN) Salarieh, H ; Alasty, A ; Sharif University of Technology
    2009
    Abstract
    In this paper based on the sliding mode concept, a nonlinear delayed feedback control is proposed for stabilizing the unstable periodic orbits (UPOs) of chaotic systems. It is assumed that the period of the desired UPO is known, but its time series and the initial conditions generated the UPO are not available. The ability of the proposed control method in stabilizing the UPO of the chaotic systems is analytically proved and the effectiveness of the method is numerically examined by applying it to the chaotic Duffing system. © 2007 Elsevier Ltd. All rights reserved  

    Chaos synchronization in a class of chaotic systems using Kalman filter and feedback linearization methods

    , Article 8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006, Torino, 4 July 2006 through 7 July 2006 ; Volume 2006 , 2006 ; 0791837793 (ISBN); 9780791837795 (ISBN) Salarieh, H ; Alasty, A ; Sharif University of Technology
    American Society of Mechanical Engineers  2006
    Abstract
    In this paper a combination of Kalman filter and feedback linearization methods is used to present a controller-identifier system for synchronizing two different chaotic systems. The drive system has some unknown parameters which are supposed to have linear form within its dynamic equation. An identifier based on Kalman filter approach is designed to estimate the unknown parameters of the drive system, and simultaneously a feedback linearizing controller is used to synchronize the chaotic behavior of the response system with the drive chaotic system. The method proposed in this paper is applied to the Lure' and the Genesio dynamic systems as the drive and response chaotic systems. The... 

    Active Learning in Image Retrieval

    , M.Sc. Thesis Sharif University of Technology Fadaee, Mohsen (Author) ; Rabiei, Hamid Reza (Supervisor)
    Abstract
    Image retrieval, simply put, is the process of finding images in a predefined set , that are similar to an image specified by the user. In particular, the user inputs an image as query, and expects to see images similar to the query. Our purpose is to retrieve the images, by means of visual features, without any use of latent information such as tags and annotations.Afer the first round of retrieval, the answers can become more accurate, by means of user feedbacks. In this state, using active learning methods may be usefull. By using active data selection, we hope to achieve the answer faster. Learning based on manifold assumption, is another means which may be used in image retrieval.... 

    Maximal bound for output feedback gain in stabilization of fixed points of fractional-order chaotic systems

    , Article Journal of Computational and Nonlinear Dynamics ; Volume 6, Issue 3 , February , 2011 ; 15551415 (ISSN) Tavazoei, M. S ; Sharif University of Technology
    2011
    Abstract
    This paper deals with the problem of stabilizing the unstable fixed points of a class of fractional-order chaotic systems via using static output feedback. At first, a static output feedback controller designed to stabilize a fixed point of a fractional-order chaotic system is considered. Then, the maximal allowable perturbation bound around the nominal value of the output feedback gain of the designed controller, such that the stability of the intended fixed point in the closed-loop system is guaranteed, is analytically determined. Also, some numerical examples are presented to confirm the validity of the analytical results of the paper  

    Observer-Based Output Feedback Linearization Control with Application to HIV Dynamics

    , Article Industrial and Engineering Chemistry Research ; Volume 54, Issue 10 , January , 2015 , Pages 2697-2708 ; 08885885 (ISSN) Hajizadeh, I ; Shahrokhi, M ; Sharif University of Technology
    American Chemical Society  2015
    Abstract
    This paper presents the feedback linearization control of HIV infection. A multi-input multi-output (MIMO) dynamic nonlinear HIV infection model for this purpose has been used. For this purpose, three widely used drugs are considered. A Luenberger-like nonlinear observer (LNO) is designed for estimation of unavailable states. To minimize the side effects of drugs, the concentration of ZDV which has the highest side effect is fixed to a minimum value and the external controllers parameters are obtained by maximizing an objective function. In the control design, limitations on drug consumption and unavailability of all states are taken into account. The closed-loop stability has been... 

    Control of a chemical reactor with chaotic dynamics

    , Article Iranian Journal of Chemistry and Chemical Engineering ; Volume 29, Issue 4 , 2010 , Pages 149-159 ; 10219986 (ISSN) Rasoulian, S ; Shahrokhi, M ; Salarieh, H ; Sharif University of Technology
    2010
    Abstract
    In this paper, control of a non-isothermal continuous stirred tank reactor in which two parallel autocatalytic reactions take place has been addressed. The reactor shows chaotic behavior for a certain set of reactor parameters. In order to control the product concentration, an optimal state feedback controller has been designed. Since concentrations of reactor species are not measured, an observer has been designed for implementation of the proposed control scheme. The local asymptotic stability of the closed-loop system including observer dynamics has been shown via the Lyapunov stability theorem. effectiveness of the proposed controller in load rejection and set point tracking has been... 

    Achievable rates with quantised channel state information in a multiple-access channel with one cognitive transmitter

    , Article IET Communications ; Volume 4, Issue 11 , 2010 , Pages 1373-1380 ; 17518628 (ISSN) Charmchi, H ; Nasiri Kenari, M ; Sharif University of Technology
    2010
    Abstract
    The authors investigate the achievable rates of a multiple-access channel with one cognitive transmitter in a fading channel. The cognitive transmitter uses dirty-paper coding to mitigate the known interference. They assume partial transmit channel state information which is obtained through a quantised limited feedback. In this model, the receiver sends as feedback only a finite number of bits describing the fading coefficients. Numerical results show that different quantisation schemes must be used for different transmitters (cognitive and non-cognitive) in order to maximise their rates. Also, the number of quantisation bits allocated to each channel coefficient (i.e. the channels from the... 

    Stabilization of unstable fixed points of fractional-order systems by fractional-order linear controllers and its applications in suppression of chaotic oscillations

    , Article Journal of Dynamic Systems, Measurement and Control, Transactions of the ASME ; Volume 132, Issue 2 , 2010 , Pages 1-7 ; 00220434 (ISSN) Tavazoei, M. S ; Haeri, M ; Sharif University of Technology
    2010
    Abstract
    In this paper, two fractional-order linear controllers are proposed to stabilize unstable equilibrium points of a chaotic fractional-order system. The first controller is based on the dynamic output feedback control idea and requires detectability of the linearized model of the fractional-order system on the equilibrium point. The second controller is a dynamic state feedback controller and requires observability of the linearized model. In both considered cases, the stabilizability of the model is assumed. The number of inner states in the second controller is one and therefore its structure is much simpler than the first controller. To illustrate the applicability, these controllers are... 

    Fault-Tolerant control of uncertain linear systems in the presence of L∞ disturbances and actuator saturation

    , Article 4th International Conference on Control, Instrumentation, and Automation, 27 January 2016 through 28 January 2016 ; 2016 , Pages 307-312 ; 9781467387040 (ISBN) Khatibi, M ; Haeri, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    Abstract
    In this paper the fault-Tolerant control problem for uncertain linear systems in the presence of L, disturbances and actuator saturation is studied. The conflict between enlarging the domain of attraction and attenuating the effect of L, disturbances is tackled by proposing a non-constant state feedback controller. The feedback gains are calculated off-line by using linear matrix inequalities. In addition, the proposed method is capable of tolerating time-varying faults. The suggested approach is implemented on a sample model and the result is compared with other works  

    Temporal output profile of gain-coupled distributed feedback dye laser

    , Article Laser Physics ; Volume 27, Issue 8 , 2017 ; 1054660X (ISSN) Pasandideh, K ; Souri, S ; Gohari Kamel, N ; Sadighi Bonabi, R ; Sharif University of Technology
    Institute of Physics Publishing  2017
    Abstract
    The lasing mechanism and temporal output profile of distributed feedback dye lasers is investigated, using a model based on induced polarization in the dye solution, where a more accurate behavior of the laser output is predicted. It is found that the temporal output profile of the laser is mostly determined by the concentration of dye solution and the lifetime of the upper laser level of dye molecules. To a large extent, the results of this work agree with experimental studies, even at high-level pump intensities where the self Q-switched model fails to be applied. Especially, the experimentally observed irregular intensity profile of laser output is explained. It is also shown that, when... 

    Robust composite nonlinear feedback control for spacecraft rendezvous systems under parameter uncertainty, external disturbance, and input saturation

    , Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; 2018 ; 09544100 (ISSN) Namdari, H ; Allahverdizadeh, F ; Sharifi, A ; Sharif University of Technology
    SAGE Publications Ltd  2018
    Abstract
    This paper presents a new robust composite nonlinear feedback control law for accurate, smooth, and fast regulation in the presence of parameter uncertainties, external disturbances, and input saturation for a class of spacecraft rendezvous systems. The novel proposed method consists of the original composite nonlinear feedback part for good transient performance plus a nonlinear disturbance rejection part for reducing the steady-state error stemming from variable disturbances and simultaneously producing feasible control input. The nonlinear disturbance rejection relies on sliding-mode observer for disturbance estimation. Closed-loop system stability has been proved with the Lyapunov...