Proprioceptive Mechanism for Bioinspired Fish Swimming.

In this Letter, we propose a mechanism for driving bioinspired fish swimming locomotion based on proprioceptive sensing. Proprioception provides information about and representation of a body's position, motion, and acceleration in addition to the usual five senses. We hypothesize that a feedback loop based on this "sixth" sense results in an instability, driving the locomotion. In order to test our assumptions, we use a biomimetic robot and compare the experimental results to a simple yet generic model with excellent agreement.

Propulsion of liquid marbles: A tool to measure their effective surface tension and viscosity.

The effective surface tension of lycopodium-coated liquid marbles is calculated from the analysis of their free vibrations. Levitation of liquid marbles was achieved by the catapult mechanism. The effective surface tension was calculated with the Rayleigh formula for eigen-frequencies of oscillating spherical droplets. The calculated effective surface tension is close to the values, obtained by other experimental methods and supports the suggestion that the effective surface tension of lycopodium-coated marbles is markedly lower than that of the bare water/vapor interface. The analysis of damping of oscillations of levitating marbles enabled introduction of the notion of ≪effective viscosity≫ of marbles. A semi-quantitative model elucidating the energy dissipation in oscillating marbles is proposed. The scaling law describing the viscous dissipation in liquid marbles is derived and shown to be in good agreement with experimental results.

Dynamics of a ball bouncing on a vibrated elastic membrane.

We investigate the dynamics of a ball bouncing on a vibrated elastic membrane. Beyond the classical solid-solid case, we study the effect of introducing new degrees of freedom by allowing substrate oscillations. The forcing frequency of the vibration strongly influences the different thresholds between the dynamical states. The simple model proposed gives good agreement between the experiments and the analytical expression for the threshold at which the ball begins to bounce. Numerical simulations permit to qualitatively recover the experimental phase diagram. Finally, we discuss how this simple system can give new insights in the recent experimental studies on bouncing droplets.

Orbital frustration at the origin of the magnetic behavior in LiNiO2.

We report on the ESR, magnetization, and magnetic susceptibility measurements performed over a large temperature range, from 1.5 to 750 K, on high-quality stoichiometric LiNiO2. We find that this compound displays two distinct temperature regions where its magnetic behavior is anomalous. With the help of a statistical model based on the Kugel'-Khomskii Hamiltonian, we show that below T(of) approximately 400 K, an orbitally frustrated state characteristic of the triangular lattice is established. This then gives a solution to the long-standing controversial problem of the magnetic behavior in LiNiO2.

Reentrant layering in rare gas adsorption: preroughening or premelting?

The reentrant layering transition found in rare gas adsorption on solid substrates has conflictually been explained in terms either of preroughening (PR) or of top layer melting-solidification phenomena. We obtain adsorption isotherms of Lennard-Jones particles on an attractive substrate by off lattice grand canonical Monte Carlo simulation, and reproduce reentrant layering. Microscopic analysis confirms a transformation of the top surface layer from solid to quasiliquid across the transition. At the same time, however, the surface coverage is found to switch from close to one to close to half, the latter indicating a disordered flat surface and establishing PR as the underlying mechanism. We conclude that top layer melting can trigger PR. In turn, PR appears to act as the threshold transition for surface melting in rare gas solids.