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Jana Kasparova - One of the best experts on this subject based on the ideXlab platform.

  • modifications of thick Target Model re acceleration of electron beams by static and stochastic electric fields
    Astronomy and Astrophysics, 2014
    Co-Authors: M. Varady, Z. Moravec, M Karlický, Jana Kasparova
    Abstract:

    Context. The collisional thick-Target Model (CTTM) of the impulsive phase of solar flares, together with the famous CSHKP Model, presented for many years a “standard” Model, which straightforwardly explained many observational aspects of flares. On the other hand, many critical issues appear when the concept is scrutinised theoretically or with the new generation of hard X-ray (HXR) observations. The famous “electron number problem” or problems related to transport of enormous particle fluxes though the corona represent only two of them. To resolve the discrepancies, several modifications of the CTTM appeared. Aims. We study two of them based on the global and local re-acceleration of non-thermal electrons by static and stochastic electric fields during their transport from the coronal acceleration site to the thick-Target region in the chromosphere. We concentrate on a comparison of the non-thermal electron distribution functions, chromospheric energy deposits, and HXR spectra obtained for both considered modifications with the CTTM itself. Methods. The results were obtained using a relativistic test-particle approach. We simulated the transport of non-thermal electrons with a power-law spectrum including the influence of scattering, energy losses, magnetic mirroring, and also the e ects of the electric fields corresponding to both modifications of the CTTM. Results. We show that both modifications of the CTTM change the outcome of the chromospheric bombardment in several aspects. The modifications lead to an increase in chromospheric energy deposit, change of its spatial distribution, and a substantial increase in the corresponding HXR spectrum intensity. Conclusions. The re-acceleration in both Models reduces the demands on the e ciency of the primary coronal accelerator, on the electron fluxes transported from the corona downwards, and on the total number of accelerated coronal electrons during flares.

  • modifications of thick Target Model re acceleration of electron beams by static and stochastic electric fields
    arXiv: Solar and Stellar Astrophysics, 2014
    Co-Authors: M. Varady, Z. Moravec, M Karlický, Jana Kasparova
    Abstract:

    We study two modifications of the collisional thick-Target Model (CTTM) based on the global and local re-acceleration of non-thermal electrons by static and stochastic electric fields during their transport from the coronal acceleration site to the thick-Target region in the chromosphere. We concentrate on a comparison of the non-thermal electron distribution functions, chromospheric energy deposits, and HXR spectra obtained for both considered modifications with the CTTM itself. The results were obtained using a relativistic test-particle approach. We simulated the transport of non-thermal electrons with a power-law spectrum including the influence of scattering, energy losses, magnetic mirroring, and also the effects of the electric fields corresponding to both modifications of the CTTM. We show that both modifications of the CTTM change the outcome of the chromospheric bombardment in several aspects. The modifications lead to an increase in chromospheric energy deposit, change of its spatial distribution, and a substantial increase in the corresponding HXR spectrum intensity.

Farrokh Janabi-sharifi - One of the best experts on this subject based on the ideXlab platform.

  • Characteristics of robot visual servoing methods and Target Model estimation
    Proceedings of the IEEE Internatinal Symposium on Intelligent Control, 2002
    Co-Authors: Lingfeng Deng, W.j. Wilson, Farrokh Janabi-sharifi
    Abstract:

    This paper presents a review of characteristics of the two main visual servoing methods: image-based visual servoing and position-based visual servoing. First, a generic structure is defined with an emphasis on the same system inputs and outputs for the two methods. The stability, robustness, sensitivity, and other general characteristics of the methods are presented. To overcome the dependency of both methods on a known Target Model, a midpoint triangulation method is proposed to estimate the unknown Target Model for robot visual servoing.

  • IROS - Combined Target Model estimation and position-based visual servoing
    2004 IEEE RSJ International Conference on Intelligent Robots and Systems (IROS) (IEEE Cat. No.04CH37566), 1
    Co-Authors: Lingfeng Deng, W.j. Wilson, Farrokh Janabi-sharifi
    Abstract:

    In this paper, the problem of combined Target Model estimation and position-based visual servoing is addressed. The Target object is assumed to be stationary with at least 3 distinguishable feature points. The midpoint triangulation method and a rough estimation method are developed for initial estimation of the Target Model and relative pose of Target in current end-effector frame. A novel decoupled EKF-based online estimation algorithm is proposed to improve the Target Model and relative pose estimation simultaneously under continuous robot dynamic motion. This new method is robust to large initial estimation errors and provides consistent and accurate Target Model estimation for optimal pose estimation as required in position-based visual servoing. Experimental results are given to demonstrate the performance of the proposed method.

  • Decoupled EKF for simultaneous Target Model and relative pose estimation using feature points
    Proceedings of 2005 IEEE Conference on Control Applications 2005. CCA 2005., 1
    Co-Authors: Lingfeng Deng, W.j. Wilson, Farrokh Janabi-sharifi
    Abstract:

    In this paper, the problem of combined Target Model and relative pose estimation for position-based visual servoing is addressed. The Target object is assumed to be stationary with at least 3 distinguishable feature points. The midpoint triangulation method and a rough estimation method are developed for initial estimation of the Target Model and relative pose of Target in current robot end-effector frame. A novel decoupled extended Kalman Filter (EKF)-based online estimation algorithm is proposed to improve the Target Model and relative pose estimation simultaneously under continuous robot dynamic motion. This new method is robust to large initial estimation errors and provides consistent and accurate Target Model estimation for optimal pose estimation as required in position-based visual servoing. Experimental results are given to demonstrate the performance of the proposed method

M. Varady - One of the best experts on this subject based on the ideXlab platform.

  • modifications of thick Target Model re acceleration of electron beams by static and stochastic electric fields
    Astronomy and Astrophysics, 2014
    Co-Authors: M. Varady, Z. Moravec, M Karlický, Jana Kasparova
    Abstract:

    Context. The collisional thick-Target Model (CTTM) of the impulsive phase of solar flares, together with the famous CSHKP Model, presented for many years a “standard” Model, which straightforwardly explained many observational aspects of flares. On the other hand, many critical issues appear when the concept is scrutinised theoretically or with the new generation of hard X-ray (HXR) observations. The famous “electron number problem” or problems related to transport of enormous particle fluxes though the corona represent only two of them. To resolve the discrepancies, several modifications of the CTTM appeared. Aims. We study two of them based on the global and local re-acceleration of non-thermal electrons by static and stochastic electric fields during their transport from the coronal acceleration site to the thick-Target region in the chromosphere. We concentrate on a comparison of the non-thermal electron distribution functions, chromospheric energy deposits, and HXR spectra obtained for both considered modifications with the CTTM itself. Methods. The results were obtained using a relativistic test-particle approach. We simulated the transport of non-thermal electrons with a power-law spectrum including the influence of scattering, energy losses, magnetic mirroring, and also the e ects of the electric fields corresponding to both modifications of the CTTM. Results. We show that both modifications of the CTTM change the outcome of the chromospheric bombardment in several aspects. The modifications lead to an increase in chromospheric energy deposit, change of its spatial distribution, and a substantial increase in the corresponding HXR spectrum intensity. Conclusions. The re-acceleration in both Models reduces the demands on the e ciency of the primary coronal accelerator, on the electron fluxes transported from the corona downwards, and on the total number of accelerated coronal electrons during flares.

  • modifications of thick Target Model re acceleration of electron beams by static and stochastic electric fields
    arXiv: Solar and Stellar Astrophysics, 2014
    Co-Authors: M. Varady, Z. Moravec, M Karlický, Jana Kasparova
    Abstract:

    We study two modifications of the collisional thick-Target Model (CTTM) based on the global and local re-acceleration of non-thermal electrons by static and stochastic electric fields during their transport from the coronal acceleration site to the thick-Target region in the chromosphere. We concentrate on a comparison of the non-thermal electron distribution functions, chromospheric energy deposits, and HXR spectra obtained for both considered modifications with the CTTM itself. The results were obtained using a relativistic test-particle approach. We simulated the transport of non-thermal electrons with a power-law spectrum including the influence of scattering, energy losses, magnetic mirroring, and also the effects of the electric fields corresponding to both modifications of the CTTM. We show that both modifications of the CTTM change the outcome of the chromospheric bombardment in several aspects. The modifications lead to an increase in chromospheric energy deposit, change of its spatial distribution, and a substantial increase in the corresponding HXR spectrum intensity.

  • Observational consequences of the local re-acceleration thick-Target Model
    Journal of Physics: Conference Series, 2013
    Co-Authors: M. Varady, Z. Moravec, Marian Karlický, J. Kašparová
    Abstract:

    In our contribution we compare the efficiency of the hard X-ray production and the vertical sizes and positions of the hard X-ray sources for the classical collisional thick-Target Model and for its recently proposed modification, the local re-acceleration thick-Target Model. The latter Model has been proposed in order to ease some of the severe theoretical problems of the collisional thick-Target Model related to interpretation of the observational properties of the foot-point HXR sources in solar flares. The results are obtained using a relativistic test-particle approach for a fully ionised atmosphere with a converging magnetic field and a single (compact) flare loop.

Lingfeng Deng - One of the best experts on this subject based on the ideXlab platform.

  • Characteristics of robot visual servoing methods and Target Model estimation
    Proceedings of the IEEE Internatinal Symposium on Intelligent Control, 2002
    Co-Authors: Lingfeng Deng, W.j. Wilson, Farrokh Janabi-sharifi
    Abstract:

    This paper presents a review of characteristics of the two main visual servoing methods: image-based visual servoing and position-based visual servoing. First, a generic structure is defined with an emphasis on the same system inputs and outputs for the two methods. The stability, robustness, sensitivity, and other general characteristics of the methods are presented. To overcome the dependency of both methods on a known Target Model, a midpoint triangulation method is proposed to estimate the unknown Target Model for robot visual servoing.

  • IROS - Combined Target Model estimation and position-based visual servoing
    2004 IEEE RSJ International Conference on Intelligent Robots and Systems (IROS) (IEEE Cat. No.04CH37566), 1
    Co-Authors: Lingfeng Deng, W.j. Wilson, Farrokh Janabi-sharifi
    Abstract:

    In this paper, the problem of combined Target Model estimation and position-based visual servoing is addressed. The Target object is assumed to be stationary with at least 3 distinguishable feature points. The midpoint triangulation method and a rough estimation method are developed for initial estimation of the Target Model and relative pose of Target in current end-effector frame. A novel decoupled EKF-based online estimation algorithm is proposed to improve the Target Model and relative pose estimation simultaneously under continuous robot dynamic motion. This new method is robust to large initial estimation errors and provides consistent and accurate Target Model estimation for optimal pose estimation as required in position-based visual servoing. Experimental results are given to demonstrate the performance of the proposed method.

  • Decoupled EKF for simultaneous Target Model and relative pose estimation using feature points
    Proceedings of 2005 IEEE Conference on Control Applications 2005. CCA 2005., 1
    Co-Authors: Lingfeng Deng, W.j. Wilson, Farrokh Janabi-sharifi
    Abstract:

    In this paper, the problem of combined Target Model and relative pose estimation for position-based visual servoing is addressed. The Target object is assumed to be stationary with at least 3 distinguishable feature points. The midpoint triangulation method and a rough estimation method are developed for initial estimation of the Target Model and relative pose of Target in current robot end-effector frame. A novel decoupled extended Kalman Filter (EKF)-based online estimation algorithm is proposed to improve the Target Model and relative pose estimation simultaneously under continuous robot dynamic motion. This new method is robust to large initial estimation errors and provides consistent and accurate Target Model estimation for optimal pose estimation as required in position-based visual servoing. Experimental results are given to demonstrate the performance of the proposed method

W.j. Wilson - One of the best experts on this subject based on the ideXlab platform.

  • observability of planar combined relative pose and Target Model estimation using monocular vision
    Advances in Computing and Communications, 2010
    Co-Authors: Michael J Tribou, David Wang, W.j. Wilson
    Abstract:

    This paper presents an observability analysis of the relative pose estimation process used in a planar Position-Based Visual Servoing or visual Simultaneous Localization and Mapping system. The results indicate potentially problematic situations where an estimator may be unable to track the relative pose and Target object Model based on monocular camera measurements alone. A complete set of unobservable configurations for a linearized relative pose system with a general constant velocity motion Model, are determined by examining the observability matrix structure, both for the cases when the Target object Model point feature coordinates are known and unknown a priori.

  • Characteristics of robot visual servoing methods and Target Model estimation
    Proceedings of the IEEE Internatinal Symposium on Intelligent Control, 2002
    Co-Authors: Lingfeng Deng, W.j. Wilson, Farrokh Janabi-sharifi
    Abstract:

    This paper presents a review of characteristics of the two main visual servoing methods: image-based visual servoing and position-based visual servoing. First, a generic structure is defined with an emphasis on the same system inputs and outputs for the two methods. The stability, robustness, sensitivity, and other general characteristics of the methods are presented. To overcome the dependency of both methods on a known Target Model, a midpoint triangulation method is proposed to estimate the unknown Target Model for robot visual servoing.

  • IROS - Combined Target Model estimation and position-based visual servoing
    2004 IEEE RSJ International Conference on Intelligent Robots and Systems (IROS) (IEEE Cat. No.04CH37566), 1
    Co-Authors: Lingfeng Deng, W.j. Wilson, Farrokh Janabi-sharifi
    Abstract:

    In this paper, the problem of combined Target Model estimation and position-based visual servoing is addressed. The Target object is assumed to be stationary with at least 3 distinguishable feature points. The midpoint triangulation method and a rough estimation method are developed for initial estimation of the Target Model and relative pose of Target in current end-effector frame. A novel decoupled EKF-based online estimation algorithm is proposed to improve the Target Model and relative pose estimation simultaneously under continuous robot dynamic motion. This new method is robust to large initial estimation errors and provides consistent and accurate Target Model estimation for optimal pose estimation as required in position-based visual servoing. Experimental results are given to demonstrate the performance of the proposed method.

  • Decoupled EKF for simultaneous Target Model and relative pose estimation using feature points
    Proceedings of 2005 IEEE Conference on Control Applications 2005. CCA 2005., 1
    Co-Authors: Lingfeng Deng, W.j. Wilson, Farrokh Janabi-sharifi
    Abstract:

    In this paper, the problem of combined Target Model and relative pose estimation for position-based visual servoing is addressed. The Target object is assumed to be stationary with at least 3 distinguishable feature points. The midpoint triangulation method and a rough estimation method are developed for initial estimation of the Target Model and relative pose of Target in current robot end-effector frame. A novel decoupled extended Kalman Filter (EKF)-based online estimation algorithm is proposed to improve the Target Model and relative pose estimation simultaneously under continuous robot dynamic motion. This new method is robust to large initial estimation errors and provides consistent and accurate Target Model estimation for optimal pose estimation as required in position-based visual servoing. Experimental results are given to demonstrate the performance of the proposed method

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