Adiabatic invariants drive rhythmic human motion in variablegravity / Nicolas Boulanger  

Public ISBD Titre : Adiabatic invariants drive rhythmic human motion in variablegravity Type de document : document électronique Auteurs : Nicolas Boulanger ; Fabien Buisseret ; V. Dehouck ; Frédéric Dierick ; Olivier White Année de publication : 2019 Langues : Anglais (eng) Résumé : Natural human movements are stereotyped. They minimise cost functions that include energy,a natural candidate from mechanical and physiological points of view. In time-changing envi-ronments, however, motor strategies are modified since energy is no longer conserved. Adiabaticinvariants are relevant observables in such cases, although they have not been investigated in hu-man motor control so far. We fill this gap and show that the theory of adiabatic invariants explainshow humans move when gravity varies. En ligne : https://arxiv.org/pdf/1906.08686.pdf Permalink : ./index.php?lvl=notice_display&id=84496 Adiabatic invariants drive rhythmic human motion in variablegravity [document électronique] / Nicolas Boulanger ; Fabien Buisseret ; V. Dehouck ; Frédéric Dierick ; Olivier White . - 2019. Langues : Anglais (eng) Résumé : Natural human movements are stereotyped. They minimise cost functions that include energy,a natural candidate from mechanical and physiological points of view. In time-changing envi-ronments, however, motor strategies are modified since energy is no longer conserved. Adiabaticinvariants are relevant observables in such cases, although they have not been investigated in hu-man motor control so far. We fill this gap and show that the theory of adiabatic invariants explainshow humans move when gravity varies. En ligne : https://arxiv.org/pdf/1906.08686.pdf Permalink : ./index.php?lvl=notice_display&id=84496

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Higher-derivative harmonic oscillators: stability of classical dynamics and adiabatic invariants / Nicolas Boulanger in The European Physical Journal C [périodique électronique], 79 (2019)  

Public ISBD [article]  inThe European Physical Journal C [périodique électronique] > 79 (2019) Titre : Higher-derivative harmonic oscillators: stability of classical dynamics and adiabatic invariants Type de document : document électronique Auteurs : Nicolas Boulanger ; Fabien Buisseret ; Frédéric Dierick ; Olivier White Année de publication : 2019 Langues : Anglais (eng) Résumé : The status of classical stability in higher-derivative systems is still subject to discussions. In this note, we argue that, contrary to general belief, many higher-derivative systems are classically stable. The main tool to see this property are Nekhoroshev’s estimates relying on the action-angle formulation of classical mechanics. The latter formulation can be reached provided the Hamiltonian is separable, which is the case for higher-derivative harmonic oscillators. The Pais–Uhlenbeck oscillators appear to be the only type of higher-derivative harmonic oscillator with stable classical dynamics. A wide class of interaction potentials can even be added that preserve classical stability. Adiabatic invariants are built in the case of a Pais–Uhlenbeck oscillator slowly changing in time; it is shown indeed that the dynamical stability is not jeopardised by the time-dependent perturbation. En ligne : https://link.springer.com/article/10.1140/epjc/s10052-019-6569-y Permalink : ./index.php?lvl=notice_display&id=84495 [article] Higher-derivative harmonic oscillators: stability of classical dynamics and adiabatic invariants [document électronique] / Nicolas Boulanger ; Fabien Buisseret ; Frédéric Dierick ; Olivier White . - 2019. Langues : Anglais (eng) in The European Physical Journal C [périodique électronique] > 79 (2019) Résumé : The status of classical stability in higher-derivative systems is still subject to discussions. In this note, we argue that, contrary to general belief, many higher-derivative systems are classically stable. The main tool to see this property are Nekhoroshev’s estimates relying on the action-angle formulation of classical mechanics. The latter formulation can be reached provided the Hamiltonian is separable, which is the case for higher-derivative harmonic oscillators. The Pais–Uhlenbeck oscillators appear to be the only type of higher-derivative harmonic oscillator with stable classical dynamics. A wide class of interaction potentials can even be added that preserve classical stability. Adiabatic invariants are built in the case of a Pais–Uhlenbeck oscillator slowly changing in time; it is shown indeed that the dynamical stability is not jeopardised by the time-dependent perturbation. En ligne : https://link.springer.com/article/10.1140/epjc/s10052-019-6569-y Permalink : ./index.php?lvl=notice_display&id=84495

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Motor strategies and adiabatic invariants: The case of rhythmic motion in parabolic flights / Nicolas Boulanger  

Public ISBD Titre : Motor strategies and adiabatic invariants: The case of rhythmic motion in parabolic flights Type de document : document électronique Auteurs : Nicolas Boulanger ; Fabien Buisseret ; V. Dehouck ; Frédéric Dierick ; Olivier White Année de publication : 2021 Langues : Anglais (eng) Mots-clés : mécanique  gravitation  contrôle moteur Résumé : The role of gravity in human motor control is at the same time obvious and difficult to isolate. It can be assessed by performing experiments in variable gravity. We propose that adiabatic invariant theory may be used to reveal nearly-conserved quantities in human voluntary rhythmic motion,an individual being seen as a complex time-dependent dynamical system with bounded motion in phase-space. We study an explicit realization of our proposal: An experiment in which we asked participants to perform ∞− shaped motion of their right arm during a parabolic flight, either at self-selected pace or at a metronome’s given pace. Gravity varied between 0 and 1.8 g during a parabola. We compute the adiabatic invariants in participant’s frontal plane assuming a separable dynamics. It appears that the adiabatic invariant in vertical direction increases linearly with g, in agreement with our model. Differences between the free and metronome-driven conditions show that participants’ adaptation to variable gravity is maximal without constraint. Furthermore, motion in the participant’s transverse plane induces trajectories that may be linked to higher-derivative dynamics. Our results show that adiabatic invariants are relevant quantities to show the changes in motor strategy in time-dependent environments. En ligne : https://luck.synhera.be/bitstream/handle/123456789/1525/2104.14252.pdf?sequence= [...] Permalink : ./index.php?lvl=notice_display&id=98151 Motor strategies and adiabatic invariants: The case of rhythmic motion in parabolic flights [document électronique] / Nicolas Boulanger ; Fabien Buisseret ; V. Dehouck ; Frédéric Dierick ; Olivier White . - 2021. Langues : Anglais (eng) Mots-clés : mécanique  gravitation  contrôle moteur Résumé : The role of gravity in human motor control is at the same time obvious and difficult to isolate. It can be assessed by performing experiments in variable gravity. We propose that adiabatic invariant theory may be used to reveal nearly-conserved quantities in human voluntary rhythmic motion,an individual being seen as a complex time-dependent dynamical system with bounded motion in phase-space. We study an explicit realization of our proposal: An experiment in which we asked participants to perform ∞− shaped motion of their right arm during a parabolic flight, either at self-selected pace or at a metronome’s given pace. Gravity varied between 0 and 1.8 g during a parabola. We compute the adiabatic invariants in participant’s frontal plane assuming a separable dynamics. It appears that the adiabatic invariant in vertical direction increases linearly with g, in agreement with our model. Differences between the free and metronome-driven conditions show that participants’ adaptation to variable gravity is maximal without constraint. Furthermore, motion in the participant’s transverse plane induces trajectories that may be linked to higher-derivative dynamics. Our results show that adiabatic invariants are relevant quantities to show the changes in motor strategy in time-dependent environments. En ligne : https://luck.synhera.be/bitstream/handle/123456789/1525/2104.14252.pdf?sequence= [...] Permalink : ./index.php?lvl=notice_display&id=98151

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