Enhanced diffusion and non-Gaussian dynamics in driven magnetic nanoparticles

We investigate the out-of-equilibrium dynamics of paramagnetic colloidal nanoparticles driven above a triangular lattice of cylindrical ferromagnetic domains. We use an external precessing magnetic field to create a dynamic energy landscape which propels the particles along complex trajectories, characterized by an alternation of periodic orbital motion (localization) and stochastic particle jumping between nearest domains. We show that this system is populated by localized particles as well as delocalized (transported) ones, and tune their relative fraction via the field cone angle. Our driven system presents enhanced diffusive dynamics and an emergent non-Gaussian behavior which can be explained by considering two coexisting dynamic transport modes

Analysis of the “Sonar Hopf” Cochlea

The “Sonar Hopf” cochlea is a recently much advertised engineering design of an auditory sensor. We analyze this approach based on a recent description by its inventors Hamilton, Tapson, Rapson, Jin, and van Schaik, in which they exhibit the “Sonar Hopf” model, its analysis and the corresponding hardware in detail. We identify problems in the theoretical formulation of the model and critically examine the claimed coherence between the described model, the measurements from the implemented hardware, and biological data

At grammatical faculty of language, flies outsmart men

Using a symbolic dynamics and a surrogate data approach, we show that the language exhibited by common fruit flies Drosophila (‘D.’) during courtship is as grammatically complex as the most complex human-spoken modern languages. This finding emerges from the study of fifty high-speed courtship videos (generally of several minutes duration) that were visually frame-by-frame dissected into 37 fundamental behavioral elements. From the symbolic dynamics of these elements, the courtship-generating language was determined with extreme confidence (significance level > 0.95). The languages categorization in terms of position in Chomsky’s hierarchical language classification allows to compare Drosophila’s body language not only with computer’s compiler languages, but also with human-spoken languages. Drosophila’s body language emerges to be at least as powerful as the languages spoken by humans

Dynamics and clogging of colloidal monolayers magnetically driven through a heterogeneous landscape

We combine experiments and numerical simulations to investigate the emergence of clogging in a system of interacting paramagnetic colloidal particles driven against a disordered landscape of larger obstacles. We consider a single aperture in a landscape of immobile silica particles which are irreversibly attached to the substrate. We use an external rotating magnetic field to generate a traveling wave potential which drives the magnetic particles against these obstacles at a constant and frequency tunable speed. Experimentally we find that the particles display an intermittent dynamics with power law distributions at high frequencies. We reproduce these results by using numerical simulations and show that clogging in our system arises at large frequency, when the particles desynchronize with the moving landscape. Further, we use the model to explore the hidden role of flexibility in the obstacle displacements and the effect of hydrodynamic interactions between the particles. We also consider numerically the situation of a straight wall and investigate the range of parameters where clogging emerges in such case. Our work provides a soft matter test-bed system to investigate the effect of clogging in driven microscale matter

Effect of random-walk grammar on closed cycles.

<p>A) Histogram of the cumulative number of closed cycles across all data files from a) in a t-3 random walk model of the data, b) in t-3, t-2, t-1 random walk model according to the data’s classification,. The experimental data (“exp”) with 468 cycles fits well only into the t-3, t-2, t-1 model. Histograms are based on 100 simulations for each experimental file. B) Distribution of t-3, of t-2, of t-1 classifications a) across all experiments, b) across all experiments with females, c) across all experiments with normal males, where the absolute numbers are exhibited.</p

Comparison of experimental files to grammar-generated files.

<p>A) For each experimental symbol string, strings with the identical symbol probabilities are generated using a t-3 random walk. B) For each string (observed and simulated), is calculated. Thick red lines: experiments, thin lines: t-3 random walks. numbers the experiment. C) Red dots: for the experimental files. Blue dots: Mean values of from t-3 random walks. Bars: One standard deviation. For two thirds of all files, the t-3 model fails.</p

Example of an experiment that requires a t-1 random walk (E = 23).

<p>A) Improvement of the modeling by going from t-3 via t-2 to t-1 random walks. B) for each experiment and its surrogate set. Red dots: experiments. Blue: dots: mean values of t-3 random walks; bars: one standard deviation. Green: mean values of t-3, t-2, t-1 random walks; bars: one standard deviation. Some blue dots and bars are obscured by red and green dots and green bars. One can clearly see that the green dots approximate the experimental red dots much better than the blue dots.</p