970 research outputs found
Locating the sets of exceptional points in dissipative systems and the self-stability of bicycles
Sets in the parameter space corresponding to complex exceptional points have high codimension and by this reason they are difficult objects for numerical location. However, complex EPs play an important role in the problems of stability of dissipative systems where they are frequently considered as precursors to instability. We propose to locate the set of complex EPs using the fact that the global minimum of the spectral abscissa of a polynomial is attained at the EP of the highest possible order. Applying this approach to the problem of self-stabilization of a bicycle we find explicitly the EP sets that suggest scaling laws for the design of robust bikes that agree with the design of the known experimental machines
Robust synchronization of heterogeneous robot swarms on the sphere
Synchronization on the sphere is important to certain control applications in
swarm robotics. Of recent interest is the Lohe model, which generalizes the
Kuramoto model from the circle to the sphere. The Lohe model is mainly studied
in mathematical physics as a toy model of quantum synchronization. The model
makes few assumptions, wherefore it is well-suited to represent a swarm.
Previous work on this model has focused on the cases of complete and acyclic
networks or the homogeneous case where all oscillator frequencies are equal.
This paper concerns the case of heterogeneous oscillators connected by a
non-trivial network. We show that any undesired equilibrium is exponentially
unstable if the frequencies satisfy a given bound. This property can also be
interpreted as a robustness result for small model perturbations of the
homogeneous case with zero frequencies. As such, the Lohe model is a good
choice for control applications in swarm robotics
Optimal synchronization of Kuramoto oscillators: a dimensional reduction approach
A recently proposed dimensional reduction approach for studying
synchronization in the Kuramoto model is employed to build optimal network
topologies to favor or to suppress synchronization. The approach is based in
the introduction of a collective coordinate for the time evolution of the phase
locked oscillators, in the spirit of the Ott-Antonsen ansatz. We show that the
optimal synchronization of a Kuramoto network demands the maximization of the
quadratic function , where stands for the vector of
the natural frequencies of the oscillators, and for the network Laplacian
matrix. Many recently obtained numerical results can be re-obtained
analytically and in a simpler way from our maximization condition. A
computationally efficient {hill climb} rewiring algorithm is proposed to
generate networks with optimal synchronization properties. Our approach can be
easily adapted to the case of the Kuramoto models with both attractive and
repulsive interactions, and again many recent numerical results can be
rederived in a simpler and clearer analytical manner.Comment: 6 pages, 6 figures, final version to appear in PR
Hamiltonian dynamics and spectral theory for spin-oscillators
We study the Hamiltonian dynamics and spectral theory of spin-oscillators.
Because of their rich structure, spin-oscillators display fairly general
properties of integrable systems with two degrees of freedom. Spin-oscillators
have infinitely many transversally elliptic singularities, exactly one
elliptic-elliptic singularity and one focus-focus singularity. The most
interesting dynamical features of integrable systems, and in particular of
spin-oscillators, are encoded in their singularities. In the first part of the
paper we study the symplectic dynamics around the focus-focus singularity. In
the second part of the paper we quantize the coupled spin-oscillators systems
and study their spectral theory. The paper combines techniques from
semiclassical analysis with differential geometric methods.Comment: 32 page
Improving the Spectral Efficiency of Nonlinear Satellite Systems through Time-Frequency Packing and Advanced Processing
We consider realistic satellite communications systems for broadband and
broadcasting applications, based on frequency-division-multiplexed linear
modulations, where spectral efficiency is one of the main figures of merit. For
these systems, we investigate their ultimate performance limits by using a
framework to compute the spectral efficiency when suboptimal receivers are
adopted and evaluating the performance improvements that can be obtained
through the adoption of the time-frequency packing technique. Our analysis
reveals that introducing controlled interference can significantly increase the
efficiency of these systems. Moreover, if a receiver which is able to account
for the interference and the nonlinear impairments is adopted, rather than a
classical predistorter at the transmitter coupled with a simpler receiver, the
benefits in terms of spectral efficiency can be even larger. Finally, we
consider practical coded schemes and show the potential advantages of the
optimized signaling formats when combined with iterative detection/decoding.Comment: 8 pages, 8 figure
Chaotic Dynamics Enhance the Sensitivity of Inner Ear Hair Cells
Hair cells of the auditory and vestibular systems are capable of detecting
sounds that induce sub-nanometer vibrations of the hair bundle, below the
stochastic noise levels of the surrounding fluid. Hair bundles of certain
species are also known to oscillate without external stimulation, indicating
the presence of an underlying active mechanism. We propose that chaotic
dynamics enhance the sensitivity and temporal resolution of the hair bundle
response, and provide experimental and theoretical evidence for this effect. By
varying the viscosity and ionic composition of the surrounding fluid, we are
able to modulate the degree of chaos observed in the hair bundle dynamics in
vitro. We consistently find that the hair bundle is most sensitive to a
stimulus of small amplitude when it is poised in the weakly chaotic regime.
Further, we show that the response time to a force step decreases with
increasing levels of chaos. These results agree well with our numerical
simulations of a chaotic Hopf oscillator and suggest that chaos may be
responsible for the sensitivity and temporal resolution of hair cells
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