8,271 research outputs found
Hybrid control for low-regular nonlinear systems: application to an embedded control for an electric vehicle
This note presents an embedded automatic control strategy for a low
consumption vehicle equipped with an "on/off" engine. The main difficulties are
the hybrid nature of the dynamics, the non smoothness of the dynamics of each
mode, the uncertain environment, the fast changing dynamics, and low cost/ low
consumption constraints for the control device. Human drivers of such vehicles
frequently use an oscillating strategy, letting the velocity evolve between
fixed lower and upper bounds. We present a general justification of this very
simple and efficient strategy, that happens to be optimal for autonomous
dynamics, robust and easily adaptable for real-time control strategy. Effective
implementation in a competition prototype involved in low-consumption races
shows that automatic velocity control achieves performances comparable with the
results of trained human drivers. Major advantages of automatic control are
improved robustness and safety. The total average power consumption for the
control device is less than 10 mW
Variation of bulk Lorentz factor in AGN jets due to Compton rocket in a complex photon field
Radio-loud active galactic nuclei are among the most powerful objects in the
universe. In these objects, most of the emission comes from relativistic jets
getting their power from the accretion of matter onto supermassive black holes.
However, despite the number of studies, a jet's acceleration to relativistic
speeds is still poorly understood.
It is widely known that jets contain relativistic particles that emit
radiation through several physical processes, one of them being the inverse
Compton scattering of photons coming from external sources. In the case of a
plasma composed of electrons and positrons continuously heated by the
turbulence, inverse Compton scattering can lead to relativistic bulk motions
through the Compton rocket effect. We investigate this process and compute the
resulting bulk Lorentz factor in the complex photon field of an AGN composed of
several external photon sources.
We consider various sources here: the accretion disk, the dusty torus, and
the broad line region. We take their geometry and anisotropy carefully into
account in order to numerically compute the bulk Lorentz factor of the jet at
every altitude.
The study, made for a broad range of parameters, shows interesting and
unexpected behaviors of the bulk Lorentz factor, exhibiting acceleration and
deceleration zones in the jet. We investigate the patterns of the bulk Lorentz
factor along the jet depending on the source sizes and on the observation angle
and we finally show that these patterns can induce variability in the AGN
emission with timescales going from hours to months.Comment: 12 pages, 16 figures, accepted to A&
Dynamics and Coalitions in Sequential Games
We consider N-player non-zero sum games played on finite trees (i.e.,
sequential games), in which the players have the right to repeatedly update
their respective strategies (for instance, to improve the outcome wrt to the
current strategy profile). This generates a dynamics in the game which may
eventually stabilise to a Nash Equilibrium (as with Kukushkin's lazy
improvement), and we argue that it is interesting to study the conditions that
guarantee such a dynamics to terminate.
We build on the works of Le Roux and Pauly who have studied extensively one
such dynamics, namely the Lazy Improvement Dynamics. We extend these works by
first defining a turn-based dynamics, proving that it terminates on subgame
perfect equilibria, and showing that several variants do not terminate. Second,
we define a variant of Kukushkin's lazy improvement where the players may now
form coalitions to change strategies. We show how properties of the players'
preferences on the outcomes affect the termination of this dynamics, and we
thereby characterise classes of games where it always terminates (in particular
two-player games).Comment: In Proceedings GandALF 2017, arXiv:1709.0176
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