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X-WR-CALNAME:Namur Institute For Complex Systems
X-ORIGINAL-URL:https://www.naxys.be
X-WR-CALDESC:Events for Namur Institute For Complex Systems
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DTSTART;TZID=Europe/Paris:20191003T130000
DTEND;TZID=Europe/Paris:20191003T140000
DTSTAMP:20260429T214956
CREATED:20190911T090549Z
LAST-MODIFIED:20190930T063836Z
UID:589-1570107600-1570111200@www.naxys.be
SUMMARY:Anthony Hastir (UNamur)
DESCRIPTION:Title: On stability and control of nonlinear infinite-dimensional systems \nAbstract: We consider nonlinear dynamical systems whose state evolves in an infinite-dimensional space\, typically a Hilbert space. Stability properties of an equilibrium of such systems can be deduced by looking at a Gâteaux/Fréchet linearization of the nonlinear dynamics around that equilibrium. From « Al Jamal\, R.\, Morris\, K.\, 2018\, Linearized stability of partial differential equations with application to stabilization of the Kuramoto-Sivashinsky equation\, SIAM Journal on Control and Optimization 56 (1)\, 120–147 »\, it is known that\, if the Gâteaux/Fréchet linearization generates an exponentially stable C 0 -semigroup that is Fréchet differentiable at the equilibrium\, the nonlinear dynamics will generate a locally exponentially stable C 0 – semigroup of nonlinear operators. However\, checking the Fréchet differentiability of nonlinear operators is really challenging when they are unbounded. This observation leads us to propose a weakenend definition of Fréchet differentiability by considering different norms. This allows more flexibility in the manipulation of norm inequalities\, providing Fréchet differentiability conditions that can be verified more easily. Under some appropriate assumptions\, we show how to get Fréchet differentiability of the nonlinear semigroup in a weaker sense in order to establish appropriate local exponential stability of the nonlinear system.\nWe show also that every linear and bounded perturbation added to the nonlinear dynamics preserves the Fréchet differentiability property of the nonlinear C 0 -semigroup generated by these perturbed dynamics. For instance\, this property is of primary importance when the system is controlled by means of a feedback law. Indeed\, it implies that every stabilizing feedback for the linearized dynamics will locally exponentially stabilize the nonlinear dynamics around an equilibrium. This allows to design a stabilizing controller on a linearized model instead of a nonlinear one.\nOur results are applied to a nonisothermal axial dispersion tubular reactor model for which we consider distributed LQ-optimal regulation of the temperature.
URL:https://www.naxys.be/event/anthony-hastir-unamur/
LOCATION:E25
CATEGORIES:NAXYS Seminar
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DTSTART;TZID=Europe/Paris:20191017T130000
DTEND;TZID=Europe/Paris:20191017T140000
DTSTAMP:20260429T214956
CREATED:20190911T091448Z
LAST-MODIFIED:20190930T063853Z
UID:593-1571317200-1571320800@www.naxys.be
SUMMARY:Riccardo Muolo (UNamur)
DESCRIPTION:Title: Effects of Non-normality on Turing Instability \nAbstract: Turing mechanism describes the emergence of spatial patterns in a reaction-diffusion system of two or more species: when certain conditions are matched\, a perturbation starting from a homogeneous stable state guides the system towards a nonhomogeneous one\, the celebrated Turing patterns\, following a diffusion-driven instability [1]. The classical linear stability analysis that describes such phenomenon is based on the spectra of involved the operators. However\, such analysis may fail when the involved linear operators are non-normal\, due to a transient growth [2]. Such effect is even stronger when the system is studied on a non-normal network\, i.e.\, a network whose adjacency matrix is non-normal [3]. In a recently published work [4] we have made use of such theoretical background to extend the original theory by obtaining non-normality patterns when Turing contitions are not satisfied.\nIn this seminar I will go through the main steps of this itinerary\, from classical Turing Instability to patterns of non-normality. Firstly\, I will present qualitatively the idea of Turing\, then\, after having introduced the notion of network\, I will talk about processes of diffusion on discrete support\, I will explain a recent extention of Turing Theory on symmetric network [5] and how an asymmetric topology can affect the mechanism of pattern formation [6]. Before moving to the last part\, I will introduce the concept of non-normality and its effects on the dynamics [7]. Finally\, I will present our extension of Turing Theory on non-normal networks [4] and discuss some open problems and possible future developments. \nReferences\n[1] Turing\, A.M.\, 1952. The chemical basis of morphogenesis. Phil. Trans. R. Soc. B 237\, 37–72;\n[2] Trefethen\, L.N.\, Embree\, M.\, 2005. Spectra and Pseudospectra: The Behavior of Nonnormal Matrices and Operators. Princeton University Press\, Princeton\, NJ;\n[3] Asllani\, M.\, Lambiotte\, R.\, Carletti\, T.\, 2018. Structure and dynamics of non-normal networks\, Sci. Adv. 4\, 1–8. Eaau9403;\n[4] Muolo\, R.\, Asllani\, M.\, Fanelli\, D.\, Maini\, P.K.\, Carletti\, T.\, 2019. Patterns of non-normality in networked systems. Journal of Theoretical Biology 480 81–91;\n[5] Nakao\, H.\, Mikhailov\, A.S.\, 2010. Turing patterns in network-organized activator-inhibitor systems. Nat. Phys. 6\, 544;\n[6] Asllani\, M.\, Challenger\, J.D.\, Pavone\, F.S.\, Sacconi\, L.\, Fanelli\, D.\, 2014. The theory of pattern formation on directed networks. Nat. Comm. 5\, 4517;\n[7] Asllani\, M.\, Carletti\, T.\, 2018. Topological resilience in non-normal networked systems. Phys. Rev. E 97\, 042302.
URL:https://www.naxys.be/event/riccardo-muolo/
LOCATION:E25
CATEGORIES:NAXYS Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20191024T100000
DTEND;TZID=Europe/Paris:20191024T170000
DTSTAMP:20260429T214956
CREATED:20190911T091840Z
LAST-MODIFIED:20191011T105033Z
UID:598-1571911200-1571936400@www.naxys.be
SUMMARY:naXys Research Day 2019
DESCRIPTION:Annual naXys Research Day 2019 \nWho are we? What are our specificities? \nOctober 24th 2019\nSalle Lucien Wargnies\, 41B rue du Belvédère\, 5000 Namur (Salzinnes) \nProgram\nWelcome & Introduction: 10h00-10h30: Pr. Anne-Sophie Libert \nMorning session: Interactions between Institutes of Complex Systems \n Invited speakers:  \n\n 	10h30-11h15: Pr. Diaz-Guilera\, Complex Systems of Barcelona UBICS\n 	11h15-12h00: Pr. Paul Bourgine\, Complex Systems Institute of Paris IDF\n\nLunch: 12h00-13h00  \nAfternoon session: Our research in naXys \nContributed Talk of Pole ECO: 13h00-13h30: Pr. Jean-Yves Gnabo\nContributed Talk of Pole BIO: 13h30-14h00: Pr. Frederik De Laender \nFlash-talks (3 minutes each): 14h00-15h00 \nCoffee Break: 15h00-15h30 \nContributed Talk of Pole SPACE: 15h30-16h00: Pr. Anne Lemaître\nContributed Talk of Pole ROBUST: 16h00-16h30: Julien Petit\nContributed Talk of Pole OPTI: 16h30-17h00: Dr. Yves Caudano \nConclusions \nRegistration\nRegistration is free but mandatory\, before Wednesday\, October 15th\, through the following web form. \nWe strongly encourage submissions of flash talks for all PhD students to present their research in 3 slides\, 3 minutes. PhD students will receive certificate with ECTS mention for their participation and/or presentation.
URL:https://www.naxys.be/event/naxys-research-day/
LOCATION:Salle Lucien Wargnies\, 41B rue du Belvédère\, 5000 Namur (Salzinnes)\, Belgium
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