19,396 research outputs found
Decentralized MPC based Obstacle Avoidance for Multi-Robot Target Tracking Scenarios
In this work, we consider the problem of decentralized multi-robot target
tracking and obstacle avoidance in dynamic environments. Each robot executes a
local motion planning algorithm which is based on model predictive control
(MPC). The planner is designed as a quadratic program, subject to constraints
on robot dynamics and obstacle avoidance. Repulsive potential field functions
are employed to avoid obstacles. The novelty of our approach lies in embedding
these non-linear potential field functions as constraints within a convex
optimization framework. Our method convexifies non-convex constraints and
dependencies, by replacing them as pre-computed external input forces in robot
dynamics. The proposed algorithm additionally incorporates different methods to
avoid field local minima problems associated with using potential field
functions in planning. The motion planner does not enforce predefined
trajectories or any formation geometry on the robots and is a comprehensive
solution for cooperative obstacle avoidance in the context of multi-robot
target tracking. We perform simulation studies in different environmental
scenarios to showcase the convergence and efficacy of the proposed algorithm.
Video of simulation studies: \url{https://youtu.be/umkdm82Tt0M
Moduli Entrapment with Primordial Black Holes
We argue that primordial black holes in the early universe can provide an
efficient resolution of the Brustein-Steinhardt moduli overshoot problem in
string cosmology. When the universe is created near the Planck scale, all the
available states in the theory are excited by strong interactions and
cosmological particle production. The heavy states are described in the low
energy theory as a gas of electrically and magnetically charged black holes.
This gas of black holes quickly captures the moduli which appear in the
relation between black hole masses and charges, and slows them down with their
vevs typically close to the Planck scale. From there, the modulus may slowly
roll into a valley with a positive vacuum energy, where inflation may begin.
The black hole gas will redshift away in the course of cosmic expansion, as
inflation evicts black holes out of the horizon.Comment: 14 pages latex, 7 .eps figures; v2: added references and a few
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How can a 22-pole ion trap exhibit 10 local minima in the effective potential?
The column density distribution of trapped OH ions in a 22-pole ion trap
is measured for different trap parameters. The density is obtained from
position-dependent photodetachment rate measurements. Overall, agreement is
found with the effective potential of an ideal 22-pole. However, in addition we
observe 10 distinct minima in the trapping potential, which indicate a breaking
of the 22-fold symmetry. Numerical simulations show that a displacement of a
subset of the radiofrequency electrodes can serve as an explanation for this
symmetry breaking
Towards Resolution of Hierarchy Problems in a Cosmological Context
A cosmological scenario is proposed, which simultaneously solves the mass
hierarchy and the small dark energy problem. In the present scenario an
effective gravity mass scale (inverse of the Newton's constant) increases
during the inflationary period. The small cosmological constant or the dark
energy density in the present universe is dynamically realized by introducing
two, approximately O(2) symmetric dilatons, taking the fundamental mass scale
at TeV.Comment: 12 pages, no figur
Metastability in Bubbling AdS Space
We study the dynamics of probe M5 branes with dissolved M2 charge in bubbling
geometries with SO(4) x SO(4) symmetry. These solutions were constructed by
Bena-Warner and Lin-Lunin-Maldacena and correspond to the vacua of the
maximally supersymmetric mass-deformed M2 brane theory. We find that
supersymmetric probe M2 branes polarize into M5 brane shells whose backreaction
creates an additional bubble in the geometry. We explicitly check that the
supersymmetric polarization potential agrees with the one found within the
Polchinski-Strassler approximation. The main result of this paper is that probe
M2 branes whose orientation is opposite to the background flux can polarize
into metastable M5 brane shells. These decay to a supersymmetric configuration
via brane-flux annihilation. Our findings suggest the existence of metastable
states in the mass-deformed M2 brane theory.Comment: 38 pages, 8 figure
Anamorphosis in hybrid inflation: How to avoid fine-tuning of initial conditions?
In order to generate more than 60 e-folds of accelerated expansion in
original hybrid inflation, 2-fields trajectories are usually required to be
initially fine-tuned in a very narrow band along the inflationary valley or in
some isolated points outside it. From a more precise investigation of the
dynamics, these points which can cover a non-negligible proportion of the space
of sub-planckian initial field values, depending on the potential parameters,
are shown to be organised in connected domains with fractal boundaries. They
correspond to trajectories first falling towards the bottom of the potential,
then climbing and slow-rolling back along the inflationary valley. The full
parameter space, including initial velocities and all the potential parameters,
is then explored by using Monte-Carlo-Markov-Chains (MCMC) methods. Results
indicate that successful initial conditions (IC) outside the valley are not
localized in the parameter space and are the dominant way to realise inflation,
independently of initial field velocities. Natural bounds on parameters are
deduced. The genericity of our results is confirmed in 5 other hybrid models
from various framework.Comment: AIP Proceedings of the "Invisible Universe" conference, Palais de
l'Unesco, Paris, 29 June - 4 July 200
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