The Experts below are selected from a list of 219 Experts worldwide ranked by ideXlab platform
Åke Västermark - One of the best experts on this subject based on the ideXlab platform.
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Reply to Braasch and Postlethwait: Evolutionary origin of the teleost A2 agouti genes (agouti signaling protein 2 and agouti-related protein 2) remains unclear
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Helgi B. Schiöth, Åke VästermarkAbstract:Tetrapods express one agouti gene [agouti signaling protein (asip)] in the skin regulating pigmentation and a second [agouti-related protein (agrp)] in the brain regulating energy homeostasis. In contrast, most teleosts have four genes encoding agouti-type proteins. Braasch and Postlethwait (1) present an analysis of the evolutionary history of agouti genes in teleosts, reordering the phylogenetic tree proposed previously (2) and proposing a nomenclature change. However, gene nomenclature derives mainly from functional or sequence properties and not from evolutionary predictions. Furthermore, inclusion of an ancient agouti sequence from the elephant shark provides an additional interpretation of the phylogeny (Fig. 1).
Bo Wahlberg - One of the best experts on this subject based on the ideXlab platform.
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ON ITERATIVE FEEDBACK TUNING AND DISTURBANCE REJECTION USING SIMPLE NOISE MODELS
2008Co-Authors: Bo WahlbergAbstract:Abstract: The objective of this contribution is to discuss three basic control design methods for disturbance rejection. The key idea is to use a simple fixed continuous time noise model as a design variable to specify the desirable closed loop properties, e.g., the closed loop bandwidth. We will study three closely related controller design methods based on the noise model, namely minimum variance control, weighted minimum variance control and a loop shaping design procedure proposed by Skogestad and Postlethwaite. All these methods lead to simple controller structures, where the transfer function of the input/output relation is the only unknown part. The main motivation of this study has been tuning of controllers for disturbance rejection by means of iterative feedback tuning (IFT). Here, the controller parameters are found by minimizing a specified cost function using gradient search techniques. The gradients are estimated using data from iterative experiments. This is a rather difficult problem if no external input excitation is allowed. Import factors for good results are the controller parametrization and the choice of cost function. We propose an IFT cost function based on a simple output signal weighting tailored to the fixed noise model controller structure. This leads to robust procedure for iterative feedback tuning of a controller for disturbance rejection. The approach is illustrated on a simple example. Copyright c ○ 2005 IFA
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On iterative feedback tuning and disturbance rejection using simple noise models
'Elsevier BV', 2005Co-Authors: Bo WahlbergAbstract:The objective of this contribution is to discuss three basic control design methods for disturbance rejection. The key idea is to use a simple fixed continuous time noise model as a design variable to specify the desirable closed loop properties, e.g., the closed loop bandwidth. We will study three closely related controller design methods based on the noise model, namely minimum variance control, weighted minimum variance control and a loop shaping design procedure proposed by Skogestad and Postlethwaite. All these methods lead to simple controller structures, where the transfer function of the input/output relation is the only unknown part. The main motivation of this study has been tuning of controllers for disturbance rejection by means of iterative feedback tuning (IFT). Here, the controller parameters are found by minimizing a specified cost function using gradient search techniques. The gradients are estimated using data from iterative experiments. This is a rather difficult problem if no external input excitation is allowed. Import factors for good results are the controller parametrization and the choice of cost function. We propose an IFT cost function based on a simple output signal weighting tailored to the fixed noise model controller structure. This leads to robust procedure for iterative feedback tuning of a controller for disturbance rejection. The approach is illustrated on a simple example.QC 20120104. Sponsors: 16th Triennial World Congress of International; Federation of Automatic Control, IFAC 200
Helgi B. Schiöth - One of the best experts on this subject based on the ideXlab platform.
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Reply to Braasch and Postlethwait: Evolutionary origin of the teleost A2 agouti genes (agouti signaling protein 2 and agouti-related protein 2) remains unclear
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Helgi B. Schiöth, Åke VästermarkAbstract:Tetrapods express one agouti gene [agouti signaling protein (asip)] in the skin regulating pigmentation and a second [agouti-related protein (agrp)] in the brain regulating energy homeostasis. In contrast, most teleosts have four genes encoding agouti-type proteins. Braasch and Postlethwait (1) present an analysis of the evolutionary history of agouti genes in teleosts, reordering the phylogenetic tree proposed previously (2) and proposing a nomenclature change. However, gene nomenclature derives mainly from functional or sequence properties and not from evolutionary predictions. Furthermore, inclusion of an ancient agouti sequence from the elephant shark provides an additional interpretation of the phylogeny (Fig. 1).
Luca Zaccarian - One of the best experts on this subject based on the ideXlab platform.
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case studies using linear matrix inequalities for optimal anti windup synthesis
European Journal of Control, 2003Co-Authors: G Grimm, Matthew C Turner, Ian Postlethwaite, Andrew R Teel, Luca ZaccarianAbstract:In this paper, we present several case studies illustrating the synthesis of static and dynamic optimal finite L 2 gain anti-windup compensation using linear matrix inequalities, the theoretical underpinnings having been described in [Grimm G, Postlethwaite I, Teel AR, Turner MC, Zaccarian L. Linear matrix inequalities for full and reduced order anti-windup synthesis. American Control Conference, 2001]. The resulting performance is also compared to the well-known IMC-based anti-windup construction both through comparison of the finite L 2 gain and through simulations. The paper shows how superior performance can be obtained using optimal dynamic anti-windup schemes, as compared with optimal static schemes.
Ian Postlethwaite - One of the best experts on this subject based on the ideXlab platform.
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some new results on anti windup conditioning using the weston Postlethwaite approach
Conference on Decision and Control, 2004Co-Authors: Guido Herrmann, Matthew C Turner, Ian PostlethwaiteAbstract:Anti-windup (AW) compensation, commonly used to counteract performance and stability problems due to saturation non-linearities in the actuator of primarily linear control systems, is revisited in terms of the approach of Weston & Postlethwaite (WP second, it is shown that the most suitable choice for M is based on a plant coprime factorization; third, it is proved that the coprime factorization technique can achieve optimal performance once the designer intends to recover nominal linear controller performance for a a reasonably generic class of linear control problems. This significantly facilitates the L/sub 2/-design of full-order AW compensators. As a final result, linear matrix inequality (LMI)-design conditions for this AW-configuration are provided.
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case studies using linear matrix inequalities for optimal anti windup synthesis
European Journal of Control, 2003Co-Authors: G Grimm, Matthew C Turner, Ian Postlethwaite, Andrew R Teel, Luca ZaccarianAbstract:In this paper, we present several case studies illustrating the synthesis of static and dynamic optimal finite L 2 gain anti-windup compensation using linear matrix inequalities, the theoretical underpinnings having been described in [Grimm G, Postlethwaite I, Teel AR, Turner MC, Zaccarian L. Linear matrix inequalities for full and reduced order anti-windup synthesis. American Control Conference, 2001]. The resulting performance is also compared to the well-known IMC-based anti-windup construction both through comparison of the finite L 2 gain and through simulations. The paper shows how superior performance can be obtained using optimal dynamic anti-windup schemes, as compared with optimal static schemes.