274 research outputs found
Distributed Coverage Hole Prevention for Visual Environmental Monitoring with Quadcopters via Nonsmooth Control Barrier Functions
This paper proposes a distributed coverage control strategy for quadcopters
equipped with downward-facing cameras that prevents the appearance of
unmonitored areas in between the quadcopters' fields of view (FOVs). We derive
a necessary and sufficient condition for eliminating any unsurveilled area that
may arise in between the FOVs among a trio of quadcopters by utilizing a power
diagram, i.e. a weighted Voronoi diagram defined by radii of FOVs. Because this
condition can be described as logically combined constraints, we leverage
nonsmooth control barrier functions (NCBFs) to prevent the appearance of
unmonitored areas among a team's FOV. We then investigate the symmetric
properties of the proposed NCBFs to develop a distributed algorithm. The
proposed algorithm can support the switching of the NCBFs caused by changes of
the quadcopters composing trios. The existence of the control input satisfying
NCBF conditions is analyzed by employing the characteristics of the power
diagram. The proposed framework is synthesized with a coverage control law that
maximizes the monitoring quality while reducing overlaps of FOVs. The proposed
method is demonstrated in simulation and experiment.Comment: 17 pages, 18 figures, submitted to the IEEE Transactions on Robotic
Non-equilibrium Fluctuation Relations in a Quantum Coherent Conductor
We experimentally demonstrate the validity of non-equilibrium fluctuation
relations by using a quantum coherent conductor. In equilibrium the
fluctuation-dissipation relation leads to the correlation between current and
current noise at the conductor, namely, Johnson-Nyqusit relation. When the
conductor is voltage-biased so that the non-linear regime is entered, the
fluctuation theorem has predicted similar non-equilibrium fluctuation
relations, which hold true even when the Onsager-Casmir relations are broken in
magnetic fields. Our experiments qualitatively validate the predictions as the
first evidence of this theorem in the non-equilibrium quantum regime.
In the appendix, we give simple deduction of the higher order correlations
between the current and the current noise based on the fluctuation theorem.Comment: 4 pages, 4 figures with 1-page appendix
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