6,425 research outputs found
Lie Algebroids in Classical Mechanics and Optimal Control
We review some recent results on the theory of Lagrangian systems on Lie
algebroids. In particular we consider the symplectic and variational formalism
and we study reduction. Finally we also consider optimal control systems on Lie
algebroids and we show how to reduce Pontryagin maximum principle.Comment: This is a contribution to the Proc. of workshop on Geometric Aspects
of Integrable Systems (July 17-19, 2006; Coimbra, Portugal), published in
SIGMA (Symmetry, Integrability and Geometry: Methods and Applications) at
http://www.emis.de/journals/SIGMA
Current-driven skyrmion motion along disordered magnetic tracks
The motion of skyrmions along ferromagnetic strips driven by current pulses
is theoretically analyzed by means of micromagnetic simulations. Analytical
expressions describing the skyrmion dynamics during and after the current pulse
are obtained from an extended rigid skyrmion model, and its predictions are
compared with full micromagnetic simulations for perfect samples with a
remarkable agreement. The dynamics along realistic samples with random disorder
is also studied by both models. Our analysis describes the relevant ingredients
behind the current-driven skyrmion dynamics, and it is expected to be useful to
understand recent and future experimental.Comment: Micromagnetic simulations and analytical expressions describing the
dynamics of skyrmions under current-pulses along realistic strip
Particle detectors and the zero mode of a quantum field
We study the impact of the zero-mode of a quantum field on the evolution of a
particle detector. For a massless scalar field in a periodic cavity, we show
that the impact of the zero mode on the Unruh-DeWitt detector and its
derivative-coupling generalisation is necessarily nonvanishing but can be made
negligible in some limits, including those commonly occurring in
non-relativistic quantum optics. For the derivative-coupling detector this can
be accomplished by just tuning the zero mode's initial state, but the standard
Unruh-DeWitt detector requires a more subtle and careful tuning. Applications
include an inertial detector with arbitrary velocity, where we demonstrate the
regularity of the ultrarelativistic limit, and a detector with uniform
acceleration.Comment: 14 pages, 3 Figures. RevTex 4.1. v2: Added journal reference and
minor edits to match published versio
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