The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
H. Nahavandchi - One of the best experts on this subject based on the ideXlab platform.
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The direct topographical correction in gravimetric geoid determination by the stokes-helmert method
Journal of Geodesy, 2000Co-Authors: H. NahavandchiAbstract:The direct topographical correction is composed of both local effects and long-wavelength contributions. This implies that the Classical Integral formula for determining the direct effect may have some numerical problems in representing these different signals. On the other hand, a representation by a set of harmonic coefficients of the topography to, say, degree and order 360 will omit significant short-wavelength signals. A new formula is derived by combining the Classical formula and a set of spherical harmonics. Finally, the results of this solution are compared with the Moritz topographical correction in a test area.
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On the indirect effect in the Stokes–Helmert method of geoid determination
Journal of Geodesy, 1999Co-Authors: Lars Erik Sjöberg, H. NahavandchiAbstract:The Classical Integral formula for determining the indirect effect in connection with the Stokes–Helmert method is related to a planar approximation of the sea level. A strict Integral formula, as well as some approximations to it, are derived. It is concluded that the cap- size truncated Integral formulas will suffer from the omission of some long-wavelength contributions, of the order of 50 cm in high mountains for the Classical formula. This long-wavelength information can be represented by a set of spherical harmonic coefficients of the topography to, say, degree and order 360. Hence, for practical use, a combination of the Classical formula and a set of spherical harmonics is recommended.
Joseph A Ball - One of the best experts on this subject based on the ideXlab platform.
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schur agler and herglotz agler classes of functions positive kernel decompositions and transfer function realizations
Advances in Mathematics, 2015Co-Authors: Joseph A Ball, Dmitry S KaliuzhnyiverbovetskyiAbstract:Abstract We discuss transfer-function realization for multivariable holomorphic functions mapping the unit polydisk or the right polyhalfplane into the operator analogue of either the unit disk or the right halfplane (Schur/Herglotz functions over either the unit polydisk or the right polyhalfplane) which satisfy the appropriate stronger contractive/positive real part condition for the values of these functions on commutative tuples of strict contractions/strictly accretive operators (Schur–Agler/Herglotz–Agler functions over either the unit polydisk or the right polyhalfplane). As originally shown by Agler, the first case (polydisk to disk) can be solved via unitary extensions of a partially defined isometry constructed in a canonical way from a kernel decomposition for the function (the lurking-isometry method ). We show how a geometric reformulation of the lurking-isometry method (embedding of a given isotropic subspace of a Kreĭn space into a Lagrangian subspace—the lurking-isotropic-subspace method ) can be used to handle the second two cases (polydisk to halfplane and polyhalfplane to disk), as well as the last case (polyhalfplane to halfplane) if an additional growth condition at ∞ is imposed. For the general fourth case, we show how a linear-fractional-transformation change of variable can be used to arrive at the appropriate symmetrized nonhomogeneous Bessmertnyĭ long-resolvent realization. We also indicate how this last result recovers the Classical Integral representation formula for scalar-valued holomorphic functions mapping the right halfplane into itself.
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Schur–Agler and Herglotz–Agler classes of functions: Positive-kernel decompositions and transfer-function realizations
Advances in Mathematics, 2015Co-Authors: Joseph A Ball, Dmitry S. Kaliuzhnyi-verbovetskyiAbstract:Abstract We discuss transfer-function realization for multivariable holomorphic functions mapping the unit polydisk or the right polyhalfplane into the operator analogue of either the unit disk or the right halfplane (Schur/Herglotz functions over either the unit polydisk or the right polyhalfplane) which satisfy the appropriate stronger contractive/positive real part condition for the values of these functions on commutative tuples of strict contractions/strictly accretive operators (Schur–Agler/Herglotz–Agler functions over either the unit polydisk or the right polyhalfplane). As originally shown by Agler, the first case (polydisk to disk) can be solved via unitary extensions of a partially defined isometry constructed in a canonical way from a kernel decomposition for the function (the lurking-isometry method ). We show how a geometric reformulation of the lurking-isometry method (embedding of a given isotropic subspace of a Kreĭn space into a Lagrangian subspace—the lurking-isotropic-subspace method ) can be used to handle the second two cases (polydisk to halfplane and polyhalfplane to disk), as well as the last case (polyhalfplane to halfplane) if an additional growth condition at ∞ is imposed. For the general fourth case, we show how a linear-fractional-transformation change of variable can be used to arrive at the appropriate symmetrized nonhomogeneous Bessmertnyĭ long-resolvent realization. We also indicate how this last result recovers the Classical Integral representation formula for scalar-valued holomorphic functions mapping the right halfplane into itself.
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schur agler and herglotz agler classes of functions positive kernel decompositions and transfer function realizations
arXiv: Functional Analysis, 2013Co-Authors: Joseph A Ball, Dmitry S KaliuzhnyiverbovetskyiAbstract:We discuss transfer-function realization for multivariable holomorphic functions mapping the unit polydisk or the right polyhalfplane into the operator analogue of either the unit disk or the right halfplane (Schur/Herglotz functions over either the unit polydisk or the right polyhalfplane) which satisfy the appropriate stronger contractive/positive real part condition for the values of these functions on commutative tuples of strict contractions/strictly accretive operators (Schur--Agler/Herglotz--Agler functions over either the unit polydisk or the right polyhalfplane). As originally shown by Agler, the first case (polydisk to disk) can be solved via unitary extensions of a partially defined isometry constructed in a canonical way from a kernel decomposition for the function (the {\em lurking-isometry method}). We show how a geometric reformulation of the lurking-isometry method (embedding of a given isotropic subspace of a Kre\u{\i}n space into a Lagrangian subspace---the {\em lurking-isotropic-subspace method}) can be used to handle the second two cases (polydisk to halfplane and polyhalfplane to disk), as well as the last case (polyhalfplane to halfplane) if an additional growth condition at $\infty$ is imposed. For the general fourth case, we show how a linear-fractional-transformation change of variable can be used to arrive at the appropriate symmetrized nonhomogeneous Bessmertny\u{\i} long-resolvent realization. We also indicate how this last result recovers the Classical Integral representation formula for scalar-valued holomorphic functions mapping the right halfplane into itself.
Dmitry S Kaliuzhnyiverbovetskyi - One of the best experts on this subject based on the ideXlab platform.
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schur agler and herglotz agler classes of functions positive kernel decompositions and transfer function realizations
Advances in Mathematics, 2015Co-Authors: Joseph A Ball, Dmitry S KaliuzhnyiverbovetskyiAbstract:Abstract We discuss transfer-function realization for multivariable holomorphic functions mapping the unit polydisk or the right polyhalfplane into the operator analogue of either the unit disk or the right halfplane (Schur/Herglotz functions over either the unit polydisk or the right polyhalfplane) which satisfy the appropriate stronger contractive/positive real part condition for the values of these functions on commutative tuples of strict contractions/strictly accretive operators (Schur–Agler/Herglotz–Agler functions over either the unit polydisk or the right polyhalfplane). As originally shown by Agler, the first case (polydisk to disk) can be solved via unitary extensions of a partially defined isometry constructed in a canonical way from a kernel decomposition for the function (the lurking-isometry method ). We show how a geometric reformulation of the lurking-isometry method (embedding of a given isotropic subspace of a Kreĭn space into a Lagrangian subspace—the lurking-isotropic-subspace method ) can be used to handle the second two cases (polydisk to halfplane and polyhalfplane to disk), as well as the last case (polyhalfplane to halfplane) if an additional growth condition at ∞ is imposed. For the general fourth case, we show how a linear-fractional-transformation change of variable can be used to arrive at the appropriate symmetrized nonhomogeneous Bessmertnyĭ long-resolvent realization. We also indicate how this last result recovers the Classical Integral representation formula for scalar-valued holomorphic functions mapping the right halfplane into itself.
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schur agler and herglotz agler classes of functions positive kernel decompositions and transfer function realizations
arXiv: Functional Analysis, 2013Co-Authors: Joseph A Ball, Dmitry S KaliuzhnyiverbovetskyiAbstract:We discuss transfer-function realization for multivariable holomorphic functions mapping the unit polydisk or the right polyhalfplane into the operator analogue of either the unit disk or the right halfplane (Schur/Herglotz functions over either the unit polydisk or the right polyhalfplane) which satisfy the appropriate stronger contractive/positive real part condition for the values of these functions on commutative tuples of strict contractions/strictly accretive operators (Schur--Agler/Herglotz--Agler functions over either the unit polydisk or the right polyhalfplane). As originally shown by Agler, the first case (polydisk to disk) can be solved via unitary extensions of a partially defined isometry constructed in a canonical way from a kernel decomposition for the function (the {\em lurking-isometry method}). We show how a geometric reformulation of the lurking-isometry method (embedding of a given isotropic subspace of a Kre\u{\i}n space into a Lagrangian subspace---the {\em lurking-isotropic-subspace method}) can be used to handle the second two cases (polydisk to halfplane and polyhalfplane to disk), as well as the last case (polyhalfplane to halfplane) if an additional growth condition at $\infty$ is imposed. For the general fourth case, we show how a linear-fractional-transformation change of variable can be used to arrive at the appropriate symmetrized nonhomogeneous Bessmertny\u{\i} long-resolvent realization. We also indicate how this last result recovers the Classical Integral representation formula for scalar-valued holomorphic functions mapping the right halfplane into itself.
Tarek Hassan Mohamed - One of the best experts on this subject based on the ideXlab platform.
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distributed load frequency control in an interconnected power system using ecological technique and coefficient diagram method
International Journal of Electrical Power & Energy Systems, 2016Co-Authors: Tarek Hassan Mohamed, G Shabib, Hossam AliAbstract:Abstract This paper presents a load frequency control (LFC) design, using both of coefficient diagram method (CDM) and ecological optimal technique (ECO) in a multi-area power system. The proposed controller has been designed to reduce the effect of uncertainties owing to variations in the parameters of governors and turbines as well as load disturbance. Each local area controller is designed independently, such that, stability of the overall closed-loop system is guaranteed. The CDM structure is built on the frequency response model of multi-area power system, and physical constraints of the governors and turbines are considered. Also, the standard Kalman filter technique has been employed to estimate the full states of the system including the area frequency deviation, these states has been employed by the (ECO) state feedback optimal controller to produce the optimal control signal. Digital simulations for three-area power systems are provided to validate the effectiveness of the proposed scheme. From the simulation results, it is shown that, considering the overall closed-loop system performance with the proposed CDM + ECO technique, robustness is demonstrated in the face of uncertainties due to governors, turbines parameters variation and loads disturbances. A performance comparison between the proposed controller, CDM alone, and a Classical Integral controller (I) scheme is carried out, confirming the superiority of the proposed CDM + ECO technique.
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decentralized load frequency control in an interconnected power system using coefficient diagram method
International Journal of Electrical Power & Energy Systems, 2014Co-Authors: Michael Z Bernard, Tarek Hassan Mohamed, Yaser Qudaih, Yasunori MitaniAbstract:Abstract This paper presents a new load frequency control (LFC) design, using the Coefficient Diagram Method (CDM) in a multi-area power system. The CDM controller has been designed to reduce the effect of uncertainties owing to variations in the parameters of governors and turbines as well as load disturbance. Each local area controller is designed independently, such that, stability of the overall closed-loop system is guaranteed. The CDM structure is built on the frequency response model of multi-area power system, and physical constraints of the governors and turbines are considered. Digital simulations for both two and three-area power systems are provided to validate the effectiveness of the proposed scheme. From the simulation results it is shown that, considering the overall closed-loop system performance with the proposed CDM technique, robustness is demonstrated in the face of uncertainties due to governors and turbines parameters variation and loads disturbances. A performance comparison between the proposed controller, model predictive controllers (MPC), and a Classical Integral control (I) scheme is carried out, confirming the superiority of the proposed CDM technique.
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model predictive based load frequency control_design concerning wind turbines
International Journal of Electrical Power & Energy Systems, 2012Co-Authors: Tarek Hassan Mohamed, Hassan Bevrani, Jorge Morel, Takashi HiyamaAbstract:Abstract This paper presents a load frequency control (LFC) design using the model predictive control (MPC) technique in a multi-area power system in the presence of wind turbines. In the studied system, each local area controller is designed independently such that stability of the overall closed loop system is guaranteed. A frequency response model of multi-area power system including wind turbines is introduced. A physical constraints of the governors and turbines are considered in the model. The model was employed in the MPC structures. Digital simulations for a two area power system are provided to validate the effectiveness of the proposed scheme. The results show that, with the proposed MPC technique, the overall closed loop system performance demonstrated robustness in the face of uncertainties due to governors and turbines parameters variation and load disturbances. Also, it was denoted that wind turbine has a positive effect on the total response of the system. A performance comparison between the proposed controller with and without the participation of the wind turbines and a Classical Integral control scheme is carried out for confirming the superiority of the proposed MPC technique in the presence of the participation of the wind turbines.
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decentralized model predictive based load frequency control in an interconnected power system
Energy Conversion and Management, 2011Co-Authors: Tarek Hassan Mohamed, Hassan Bevrani, A A Hassan, Takashi HiyamaAbstract:This paper presents a new load frequency control (LFC) design using the model predictive control (MPC) technique in a multi-area power system. The MPC technique has been designed such that the effect of the uncertainty due to governor and turbine parameters variation and load disturbance is reduced. Each local area controller is designed independently such that stability of the overall closed-loop system is guaranteed. A frequency response model of multi-area power system is introduced, and physical constraints of the governors and turbines are considered. The model was employed in the MPC structures. Digital simulations for both two and three-area power systems are provided to validate the effectiveness of the proposed scheme. The results show that, with the proposed MPC technique, the overall closed-loop system performance demonstrated robustness in the face of uncertainties due to governors and turbines parameters variation and loads disturbances. A performance comparison between the proposed controller and a Classical Integral control scheme is carried out confirming the superiority of the proposed MPC technique.
Lars Erik Sjöberg - One of the best experts on this subject based on the ideXlab platform.
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On the indirect effect in the Stokes–Helmert method of geoid determination
Journal of Geodesy, 1999Co-Authors: Lars Erik Sjöberg, H. NahavandchiAbstract:The Classical Integral formula for determining the indirect effect in connection with the Stokes–Helmert method is related to a planar approximation of the sea level. A strict Integral formula, as well as some approximations to it, are derived. It is concluded that the cap- size truncated Integral formulas will suffer from the omission of some long-wavelength contributions, of the order of 50 cm in high mountains for the Classical formula. This long-wavelength information can be represented by a set of spherical harmonic coefficients of the topography to, say, degree and order 360. Hence, for practical use, a combination of the Classical formula and a set of spherical harmonics is recommended.