41,288 research outputs found
Multiple chaotic central pattern generators with learning for legged locomotion and malfunction compensation
An originally chaotic system can be controlled into various periodic
dynamics. When it is implemented into a legged robot's locomotion control as a
central pattern generator (CPG), sophisticated gait patterns arise so that the
robot can perform various walking behaviors. However, such a single chaotic CPG
controller has difficulties dealing with leg malfunction. Specifically, in the
scenarios presented here, its movement permanently deviates from the desired
trajectory. To address this problem, we extend the single chaotic CPG to
multiple CPGs with learning. The learning mechanism is based on a simulated
annealing algorithm. In a normal situation, the CPGs synchronize and their
dynamics are identical. With leg malfunction or disability, the CPGs lose
synchronization leading to independent dynamics. In this case, the learning
mechanism is applied to automatically adjust the remaining legs' oscillation
frequencies so that the robot adapts its locomotion to deal with the
malfunction. As a consequence, the trajectory produced by the multiple chaotic
CPGs resembles the original trajectory far better than the one produced by only
a single CPG. The performance of the system is evaluated first in a physical
simulation of a quadruped as well as a hexapod robot and finally in a real
six-legged walking machine called AMOSII. The experimental results presented
here reveal that using multiple CPGs with learning is an effective approach for
adaptive locomotion generation where, for instance, different body parts have
to perform independent movements for malfunction compensation.Comment: 48 pages, 16 figures, Information Sciences 201
Self-Annealing Dynamics in a Multistable System
A new type of dynamical behavior of a multistable system is reported. We
found that a simple non-equilibrium system can reduce its effective temperature
autonomously at a global minimum if the residual frustration at a global
minimum is small enough, which highlights an unexpected feature of
non-equilibrium multistable systems.Comment: 6 pages, Figures available upon reques
Theoretical studies of Van der Waals clusters
The vibrational energy levels of various rare gas trimers, Ar(_3), Ne(_3), He(_3), Ar(_2)Ne and Ne(_2)Ar, have been calculated using a coupled channel approach. We have compared results obtained with previous calculations. The existence of Efi-mov states in He(_3) has been investigated, and no evidence of their existence has been found. The affect of the Eckart conditions on embedding axis into a rotating-vibrating system has been investigated for several rare gas systems. A wide range of rare gas trimers have been studied, Ar(_3), He(_2)Ar, Ar(_2)He, Ar(_2)Ne and Ne(_2)Ar. For each trimer the full range of molecular motion is investigated. The low energy minima for the Ar(_n)N(_2) and Ne(_n)N(_2) systems have been found using simulated annealing search, and a gradient based minimisation technique, of a pairwise potential energy surface. Clusters with n ≥ 12 have been studied, and first solvation shells for both systems have been proposed. For each value of n, for n = 1 - 12, the first few low energy minima of the potential energy surface have been found. From these studies, we have gained a detailed understanding of the interplay of forces that determine the low energy structures for these systems. The affect of three-body interactions on the low energy minima both rare gas-N(_2) systems has been studied. In both system, rare gas-rare gas and rare gas- threebody interactions have been taken into account. This study has shown that the three-body forces have a small affect on the low energy structures of each system
Relation between quantum fluctuations and the performance enhancement of quantum annealing in a nonstoquastic Hamiltonian
We study the relation between quantum fluctuations and the significant
enhancement of the performance of quantum annealing in a mean-field
Hamiltonian. First-order quantum phase transitions were shown to be reduced to
second order by antiferromagnetic transverse interactions in a mean-field-type
many-body-interacting Ising spin system in a transverse field, which means an
exponential speedup of quantum annealing by adiabatic quantum computation. We
investigate if and how quantum effects manifest themselves around these first-
and second-order phase transitions to understand if the antiferromagnetic
transverse interactions appended to the conventional transverse-field Ising
model induce notable quantum effects. By measuring the proximity of the
semiclassical spin-coherent state to the true ground state as well as the
magnitude of the concurrence representing entanglement, we conclude that
significant quantum fluctuations exist around second-order transitions, whereas
quantum effects are much less prominent at first-order transitions. Although
the location of the transition point can be predicted by the classical picture,
system properties near the transition need quantum-mechanical descriptions for
a second-order transition but not necessarily for first order. It is also found
that quantum fluctuations are large within the ferromagnetic phase after a
second-order transition from the paramagnetic phase. These results suggest that
the antiferromagnetic transverse interactions induce marked quantum effects,
and this fact would be related to closely to the significant enhancement of the
performance of quantum annealing.Comment: 9 pages, 8 figure
Quark-based Description of Nuclear Matter with Simulated Annealing
We calculate ground-state properties of a many-quark system in the
string-flip model using variational Monte Carlo methods. The many-body
potential energy of the system is determined by finding the optimal grouping of
quarks into hadrons. This (optimal) assignment problem is solved by using the
stochastic optimization technique of simulated annealing. Results are presented
for the energy and length-scale for confinement as a function of density. These
results show how quarks clustering decreases with density and characterize the
nuclear- to quark-matter transition. We compare our results to a previously
published work with a similar model which uses, instead, a pairing approach to
the optimization problem.Comment: Latex with Revtex, 10 postscript figures (available from the
authors), SCRI-05059
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