State feedbacks without asymptotic observers and generalized PID regulators

2007 ◽  
pp. 367-384 ◽  
Author(s):  
Michel Fliess ◽  
Richard Marquez ◽  
Emmanuel Delaleau
Keyword(s):  
Asymptotic Observers

scholarly journals Observations of Hawking radiation: the Page curve and baby universes

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Donald Marolf ◽  
Henry Maxfield
Keyword(s):  
Black Holes ◽  
Quantum Systems ◽  
Late Time ◽  
Asymptotically Flat ◽  
Black Hole Information ◽  
Flat Spacetimes ◽  
The Cost ◽  
Baby Universes ◽  
Time Extrapolation ◽  
Asymptotic Observers

AbstractWe reformulate recent insights into black hole information in a manner emphasizing operationally-defined notions of entropy, Lorentz-signature descriptions, and asymptotically flat spacetimes. With the help of replica wormholes, we find that experiments of asymptotic observers are consistent with black holes as unitary quantum systems, with density of states given by the Bekenstein-Hawking formula. However, this comes at the cost of superselection sectors associated with the state of baby universes. Spacetimes studied by Polchinski and Strominger in 1994 provide a simple illustration of the associated concepts and techniques, and we argue them to be a natural late-time extrapolation of replica wormholes. The work aims to be self-contained and, in particular, to be accessible to readers who have not yet mastered earlier formulations of the ideas above.

scholarly journals Fermat’s principle in black-hole spacetimes

2018 ◽  
Vol 27 (14) ◽  
pp. 1847025 ◽  
Author(s):  
Shahar Hod
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Black Hole Spacetimes ◽  
Fermat’S Principle ◽  
Kerr Black Holes ◽  
Fermat's Principle ◽  
Asymptotic Observers

Black-hole spacetimes are known to possess closed light rings. We here present a remarkably compact theorem which reveals the physically intriguing fact that these unique null circular geodesics provide the fastest way, as measured by asymptotic observers, to circle around spinning Kerr black holes.

Asymptotic observers for bilinear systems with vector output

2008 ◽  
Vol 44 (5) ◽  
pp. 632-637 ◽  
Author(s):  
A. V. Il’in ◽  
S. K. Korovin ◽  
V. V. Fomichev
Keyword(s):  
Bilinear Systems ◽  
Asymptotic Observers

scholarly journals Geodesic stability and quasi normal modes via Lyapunov exponent for Hayward black hole

2020 ◽  
Vol 35 (30) ◽  
pp. 2050249
Author(s):  
Monimala Mondal ◽  
Parthapratim Pradhan ◽  
Farook Rahaman ◽  
Indrani Karar
Keyword(s):  
Black Hole ◽  
Lyapunov Exponent ◽  
Time Scale ◽  
Proper Time ◽  
Normal Modes ◽  
Schwarzschild Black Hole ◽  
Coordinate Time ◽  
Stability And Instability ◽  
The Stability ◽  
Asymptotic Observers

We derive proper time Lyapunov exponent [Formula: see text] and coordinate time Lyapunov exponent [Formula: see text] for a regular Hayward class of black hole. The proper time corresponds to [Formula: see text] and the coordinate time corresponds to [Formula: see text], where [Formula: see text] is measured by the asymptotic observers both for Hayward black hole and for special case of Schwarzschild black hole. We compute their ratio as [Formula: see text] for time-like geodesics. In the limit of [Formula: see text] that means for Schwarzschild black hole this ratio reduces to [Formula: see text]. Using Lyapunov exponent, we investigate the stability and instability of equatorial circular geodesics. By evaluating the Lyapunov exponent, which is the inverse of the instability time scale, we show that, in the eikonal limit, the real and imaginary parts of quasi-normal modes (QNMs) is specified by the frequency and instability time scale of the null circular geodesics. Furthermore, we discuss the unstable photon sphere and radius of shadow for this class of black hole.

scholarly journals Asymptotic Observers for a Class of Evolution Equations: A Nonlinear Approach

1997 ◽  
Vol 30 (6) ◽  
pp. 681-684
Author(s):  
Philippe Ligarius ◽  
Jean-François Couchouron
Keyword(s):  
Evolution Equations ◽  
Nonlinear Approach ◽  
Asymptotic Observers

Observability for systems with more outputs than inputs and asymptotic observers

1996 ◽  
Vol 223 (1) ◽  
pp. 47-78
Author(s):  
J. P. Gauthier ◽  
I. A. K. Kupka
Keyword(s):  
Asymptotic Observers

ASYMPTOTIC OBSERVERS FOR DISCRETE-TIME SWITCHED LINEAR SYSTEMS

2005 ◽  
Vol 38 (1) ◽  
pp. 1269-1274 ◽  
Author(s):  
Mohamed Babaali ◽  
Magnus Egerstedt
Keyword(s):  
Linear Systems ◽  
Discrete Time ◽  
Switched Linear Systems ◽  
Asymptotic Observers
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