[1] We investigate streamer formation in the troposphere, in electric fields above the breakdown threshold. With fully three-dimensional particle simulations, we study the combined effect of natural background ionization and of photo-ionization on the discharge morphology. In previous investigations based on deterministic fluid models without background ionization, so-called double-headed streamers emerged. But in our improved model, many electron avalanches start to grow at different locations. Eventually, the avalanches collectively screen the electric field in the interior of the discharge. This happens after what we call the "ionization screening time," for which we give an analytical estimate. As this time is comparable to the streamer formation time, we conclude that isolated streamers are unlikely to exist in fields well above breakdown in atmospheric air. Citation: Sun, A. B., J. Teunissen, and U. Ebert (2013), Why isolated streamer discharges hardly exist above the breakdown field in atmospheric air, Geophys. Res. Lett., 40,

Ionic polymer-metal composites have been widely used as actuators for robotic systems. In this article, we investigate and verify the characteristics of ionic polymer-metal composite actuators experimentally and theoretically. Two analytical models are utilized to analyze the performance of ionic polymer-metal composites: a linear irreversible electrodynamical model and a dynamic model. We find that the first model accurately predicts the static characteristics of the ionic polymer-metal composite according to the Onsager equations, while the second model is able to reveal the back relaxation characteristics of the ionic polymer-metal composite. We combine the static and dynamic models of the ionic polymer-metal composite and derive the transfer function for the ionic polymer-metal composite's mechanical response to an electrical signal. A driving signal with a smooth slope and a low frequency is beneficial for the power efficiency.

A new Nano Air Vehicle (NAV) configuration based on a coaxial nano rotor has been studied by ISAE. The coaxial rotor provides the thrust necessary for hovering and low speed translation flight. The major design challenge for rotary-wing NAVs is related to the difficulty of miniaturizing complex mechanisms such as a rotor cyclic pitch swashplate commonly used for controlling helicopters. The use of actuators made of smart materials is believed to allow for controlling rotary-wing NAVs in a much simpler and lighter way. The multidisciplinary subject of this complete system is separated into few parts. The studies of each subject are individually conducted before integrated in the future in order to optimize the global system. Those studies which are being carried out are shortly described in this paper.