The Experts below are selected from a list of 3657 Experts worldwide ranked by ideXlab platform
Dmitri Vassilevich - One of the best experts on this subject based on the ideXlab platform.
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ŠܹÈÐ Ò ¹ÁÒ×Ø ØÙØ für Mathematik in den Naturwissenschaften Leipzig Non-existence of a dilaton gravity action for the exact string black hole Non-existence of a dilaton gravity action for the exact string black hole
2020Co-Authors: Daniel Grumiller, Dmitri VassilevichAbstract:Abstract: We prove that no Local Diffeomorphism invariant two-dimensional theory of the metric and the dilaton without higher derivatives can describe the exact string black hole solution found a decade ago by Dijkgraaf, Verlinde and Verlinde. One of the key points in this proof is the concept of dilaton-shift invariance. We present and solve (classically) all dilaton-shift invariant theories of two-dimensional dilaton gravity. Two such models, resembling the exact string black hole and generalizing the CGHS model, are discussed explicitly
Rogelio Lozano - One of the best experts on this subject based on the ideXlab platform.
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brief nonlinear control of the reaction wheel pendulum
Automatica, 2001Co-Authors: Mark W Spong, Peter Corke, Rogelio LozanoAbstract:In this paper we introduce the Reaction Wheel Pendulum, a novel mechanical system consisting of a physical pendulum with a rotating bob. This system has several attractive features both from a pedagogical standpoint and from a research standpoint. From a pedagogical standpoint, the dynamics are the simplest among the various pendulum experiments available so that the system can be introduced to students earlier in their education. At the same time, the system is nonlinear and underactuated so that it can be used as a benchmark experiment to study recent advanced methodologies in nonlinear control, such as feedback linearization, passivity methods, backstepping and hybrid control. In this paper we discuss two control approaches for the problems of swingup and balance, namely, feedback linearization and passivity based control. We first show that the system is Locally feedback linearizable by a Local Diffeomorphism in state space and nonlinear feedback. We compare the feedback linearization control with a linear pole-placement control for the problem of balancing the pendulum about the inverted position. For the swingup problem we discuss an energy approach based on collocated partial feedback linearization, and passivity of the resulting zero dynamics. A hybrid/switching control strategy is used to switch between the swingup and the balance control. Experimental results are presented.
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nonlinear control of the reaction wheel pendulum
Faculty of Built Environment and Engineering, 2001Co-Authors: Mark W Spong, Peter Corke, Rogelio LozanoAbstract:In this paper we introduce the Reaction Wheel Pendulum, a novel mechanical system consisting of a physical pendulum with a rotating bob. This system has several attractive features both from a pedagogical standpoint and from a research standpoint. From a pedagogical standpoint, the dynamics are the simplest among the various pendulum experiments available so that the system can be introduced to students earlier in their education. At the same time, the system is nonlinear and underactuated so that it can be used as a benchmark experiment to study recent advanced methodologies in nonlinear control, such as feedback linearization, passivity methods, backstepping and hybrid control. In this paper we discuss two control approaches for the problems of swingup and balance, namely, feedback linearization and passivity based control. We first show that the system is Locally feedback linearizable by a Local Diffeomorphism in state space and nonlinear feedback. We compare the feedback linearization control with a linear pole-placement control for the problem of balancing the pendulum about the inverted position. For the swingup problem we discuss an energy approach based on collocated partial feedback linearization, and passivity of the resulting zero dynamics. A hybrid/switching control strategy is used to switch between the swingup and the balance control. Experimental results are presented.
Loray Frank - One of the best experts on this subject based on the ideXlab platform.
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The Riemann-Hilbert mapping for $\mathfrak{sl}_2$ -systems over genus two curves
'Societe Mathematique de France', 2019Co-Authors: Calsamiglia Gabriel, Deroin Bertrand, Heu Viktoria, Loray FrankAbstract:International audienceWe prove in two different ways that the monodromy map from the space of irreducible $\mathfrak{sl}_2$-differential-systems on genus two Riemann surfaces, towards the character variety of $\mathrm{SL}_2$-representations of the fundamental group, is a Local Diffeomorphism. This is motivated by a question raised by \'Etienne Ghys about Margulis' problem: existence of curves of negative Euler characteristic in compact quotients of $\mathrm{SL}_2(\mathbb{C})$
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The Riemann-Hilbert mapping for $\mathfrak{sl}_2$ -systems over genus two curves
'Societe Mathematique de France', 2019Co-Authors: Calsamiglia Gabriel, Deroin Bertrand, Heu Viktoria, Loray FrankAbstract:International audienceWe prove in two different ways that the monodromy map from the space of irreducible $\mathfrak{sl}_2$-differential-systems on genus two Riemann surfaces, towards the character variety of $\mathrm{SL}_2$-representations of the fundamental group, is a Local Diffeomorphism. This is motivated by a question raised by \'Etienne Ghys about Margulis' problem: existence of curves of negative Euler characteristic in compact quotients of $\mathrm{SL}_2(\mathbb{C})$.Nous montrons de deux manières différentes que l'application monodromie, depuis l'espace des sl 2-systèmes différentiels irréductibles sur les surfaces de Riemann de genre deux, vers la variété de caractères des SL 2-représentations du groupe fondamental, est un difféomorphisme Local. Nous montrons aussi que ce n'est plus le cas en genre supérieur. Notre travail est motivé par une question d'Étienne Ghysà propos d'un problème de Margulis : l'existence de courbes de caractéristique d'Euler négative dans les quotients compacts de SL 2 (C)
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The Riemann-Hilbert mapping for $\mathfrak{sl}_2$ -systems over genus two curves
2018Co-Authors: Calsamiglia Gabriel, Deroin Bertrand, Heu Viktoria, Loray FrankAbstract:We prove in two different ways that the monodromy map from the space of irreducible $\mathfrak{sl}_2$-differential-systems on genus two Riemann surfaces, towards the character variety of $\mathrm{SL}_2$-representations of the fundamental group, is a Local Diffeomorphism. This is motivated by a question raised by \'Etienne Ghys about Margulis' problem: existence of curves of negative Euler characteristic in compact quotients of $\mathrm{SL}_2(\mathbb{C})$.Comment: 35 pages; Accepted for publication at 'Bulletin de la Societ\'e Math\'ematique de France
Daniel Grumiller - One of the best experts on this subject based on the ideXlab platform.
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ŠܹÈÐ Ò ¹ÁÒ×Ø ØÙØ für Mathematik in den Naturwissenschaften Leipzig Non-existence of a dilaton gravity action for the exact string black hole Non-existence of a dilaton gravity action for the exact string black hole
2020Co-Authors: Daniel Grumiller, Dmitri VassilevichAbstract:Abstract: We prove that no Local Diffeomorphism invariant two-dimensional theory of the metric and the dilaton without higher derivatives can describe the exact string black hole solution found a decade ago by Dijkgraaf, Verlinde and Verlinde. One of the key points in this proof is the concept of dilaton-shift invariance. We present and solve (classically) all dilaton-shift invariant theories of two-dimensional dilaton gravity. Two such models, resembling the exact string black hole and generalizing the CGHS model, are discussed explicitly
Mark W Spong - One of the best experts on this subject based on the ideXlab platform.
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brief nonlinear control of the reaction wheel pendulum
Automatica, 2001Co-Authors: Mark W Spong, Peter Corke, Rogelio LozanoAbstract:In this paper we introduce the Reaction Wheel Pendulum, a novel mechanical system consisting of a physical pendulum with a rotating bob. This system has several attractive features both from a pedagogical standpoint and from a research standpoint. From a pedagogical standpoint, the dynamics are the simplest among the various pendulum experiments available so that the system can be introduced to students earlier in their education. At the same time, the system is nonlinear and underactuated so that it can be used as a benchmark experiment to study recent advanced methodologies in nonlinear control, such as feedback linearization, passivity methods, backstepping and hybrid control. In this paper we discuss two control approaches for the problems of swingup and balance, namely, feedback linearization and passivity based control. We first show that the system is Locally feedback linearizable by a Local Diffeomorphism in state space and nonlinear feedback. We compare the feedback linearization control with a linear pole-placement control for the problem of balancing the pendulum about the inverted position. For the swingup problem we discuss an energy approach based on collocated partial feedback linearization, and passivity of the resulting zero dynamics. A hybrid/switching control strategy is used to switch between the swingup and the balance control. Experimental results are presented.
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nonlinear control of the reaction wheel pendulum
Faculty of Built Environment and Engineering, 2001Co-Authors: Mark W Spong, Peter Corke, Rogelio LozanoAbstract:In this paper we introduce the Reaction Wheel Pendulum, a novel mechanical system consisting of a physical pendulum with a rotating bob. This system has several attractive features both from a pedagogical standpoint and from a research standpoint. From a pedagogical standpoint, the dynamics are the simplest among the various pendulum experiments available so that the system can be introduced to students earlier in their education. At the same time, the system is nonlinear and underactuated so that it can be used as a benchmark experiment to study recent advanced methodologies in nonlinear control, such as feedback linearization, passivity methods, backstepping and hybrid control. In this paper we discuss two control approaches for the problems of swingup and balance, namely, feedback linearization and passivity based control. We first show that the system is Locally feedback linearizable by a Local Diffeomorphism in state space and nonlinear feedback. We compare the feedback linearization control with a linear pole-placement control for the problem of balancing the pendulum about the inverted position. For the swingup problem we discuss an energy approach based on collocated partial feedback linearization, and passivity of the resulting zero dynamics. A hybrid/switching control strategy is used to switch between the swingup and the balance control. Experimental results are presented.