19 research outputs found
Differential susceptibility to noise of mixed Turing and Hopf modes in a photosensitive chemical medium
We report on experiments with the photosensitive chlorine dioxide-iodine-malonic acid reaction (CDIMA) when forced with a random (spatiotemporally) distributed illumination. Acting on a mixed mode consisting of oscillating spots, close enough to the Hopf and Turing codimension-two bifurcation, we observe attenuation of oscillations while the spatial pattern is preserved. Numerical simulations confirm and extend these results. All together these observations point out to a larger vulnerability of the Hopf with respect to the Turing mode when facing noise of intermediate intensity and small correlation parameters.Peer ReviewedPostprint (published version
Swimming modes of self-assembled magnetic micropropeller
Postprint (published version
Magnetically tunable bidirectional locomotion of a self-assembled nanorod-sphere propeller
Field-driven direct assembly of nanoscale matter has impact in disparate fields of science. In
microscale systems, such concept has been recently exploited to optimize propulsion in
viscous fluids. Despite the great potential offered by miniaturization, using self-assembly to
achieve transport at the nanoscale remains an elusive task. Here we show that a hybrid
propeller, composed by a ferromagnetic nanorod and a paramagnetic microsphere, can be
steered in a fluid in a variety of modes, from pusher to puller, when the pair is dynamically
actuated by a simple oscillating magnetic field. We exploit this unique design to build more
complex structures capable of carrying several colloidal cargos as microscopic trains that
quickly disassemble at will under magnetic command. In addition, our prototype can be
extended to smaller nanorods below the diffraction limit, but still dynamically reconfigurable
by the applied magnetic field.Peer ReviewedPostprint (published version
Direct measurement of Lighthill’s energetic efficiency of a minimal magnetic microswimmer
The realization of artificial microscopic swimmers able to
propel in viscous fluids is an emergent research field of fundamental
interest and vast technological applications. For
certain functionalities, the efficiency of the microswimmer
in converting the input power provided through an external
actuation into propulsive power output can be critical. Here
we use a microswimmer composed by a self-assembled
ferromagnetic rod and a paramagnetic sphere and directly
determine its swimming efficiency when it is actuated by
a swinging magnetic field. Using fast video recording and
numerical simulations we fully characterize the dynamics
of the propeller and identify the two independent degrees
of freedom which allow its propulsion. We then obtain
experimentally the Lighthill’s energetic efficiency of the
swimmer by measuring the power consumed during propulsion
and the energy required to translate the propeller at
the same speed. Finally, we discuss how the efficiency of
our microswimmer could be increased upon suitable tuning
of the different experimental parameters.Postprint (author's final draft
Noise-reversed stability of Turing patterns versus Hopf oscillations near codimension-two conditions
Pattern formation induced by noise is a celebrated phenomenon in diverse reaction-diffusion systems. Here we report numerical simulations with the Lengyel-Epstein model for the chlorine dioxide-iodine-malonic acid reaction when perturbed with an external spatiotemporal stochastic forcing in the vicinity of the Hopf and Turing codimension-two bifurcation. Competition between Turing and Hopf modes gives rise to the generation of transient Turing patterns evolving to stationary global oscillations. This situation is reversed by the introduction of external fluctuations and Turing patterns become dominant in this case. The increase in the spatial coherence is found for intermediate noise intensity and small correlation length.Peer Reviewe
Noise-reversed stability of Turing patterns versus Hopf oscillations near codimension-two conditions
Pattern formation induced by noise is a celebrated phenomenon in diverse reaction-diffusion systems. Here we report numerical simulations with the Lengyel-Epstein model for the chlorine dioxide-iodine-malonic acid reaction when perturbed with an external spatiotemporal stochastic forcing in the vicinity of the Hopf and Turing codimension-two bifurcation. Competition between Turing and Hopf modes gives rise to the generation of transient Turing patterns evolving to stationary global oscillations. This situation is reversed by the introduction of external fluctuations and Turing patterns become dominant in this case. The increase in the spatial coherence is found for intermediate noise intensity and small correlation length.Peer Reviewe
Noise-induced Brownian motion of spiral waves
We study the erratic displacement of spiral waves forced to move in a medium with random spatiotemporal excitability. Analytical work and numerical simulations are performed in relation to a kinematic scheme, assumed to describe the autowave dynamics for weakly excitable systems. Under such an approach, the Brownian character of this motion is proved and the corresponding dispersion coefficient is evaluated. This quantity shows a nontrivial dependence on the temporal and spatial correlation parameters of the external fluctuations. In particular, a resonantlike behavior is neatly evidenced in terms of the noise correlation time for the particular situation of spatially uniform fluctuations. Actually, this case turns out to be, to a large extent, exactly solvable, whereas a pair of dispersion mechanisms are discussed qualitatively and quantitatively to explain the results for the more general scenario of spatiotemporal disorder.Peer Reviewe
Differential susceptibility to noise of mixed Turing and Hopf modes in a photosensitive chemical medium
We report on experiments with the photosensitive chlorine dioxide-iodine-malonic acid reaction (CDIMA) when forced with a random (spatiotemporally) distributed illumination. Acting on a mixed mode consisting of oscillating spots, close enough to the Hopf and Turing codimension-two bifurcation, we observe attenuation of oscillations while the spatial pattern is preserved. Numerical simulations confirm and extend these results. All together these observations point out to a larger vulnerability of the Hopf with respect to the Turing mode when facing noise of intermediate intensity and small correlation parameters.Peer Reviewe
Wave pattern dynamics in fluctuating media
Analytical and numerical results on the ordering role of external random fluctuations in excitable systems are presented. Our study focuses on a simple model for excitable systems. Regular waves are created and sustained out of noise when the system is forced with random perturbations. Explicit results for the generation and dynamics of rings and targets are presented.Peer ReviewedPostprint (published version
Periodic forcing of scroll rings and control of Winfree turbulence in excitable media
By simulations of the Barkley model, action of uniform periodic nonresonant forcing on scroll rings and wave turbulence in three-dimensional excitable media is investigated. Sufficiently strong rapid forcing converts expanding scroll rings into the collapsing ones and suppresses the Winfree turbulence caused by the negative tension of wave filaments. Slow strong forcing has an opposite effect, leading to expansion of scroll rings and induction of the turbulence. These effects are explained in the framework of the phenomenological kinematic theory of scroll waves.Peer Reviewe