NASA LIVE.

Wednesday 25 November 2015

Fields of Force.

As The Meissner effect is an expulsion of a magnetic field from a superconductor during its transition to the superconducting state.
The German physicists Walther Meissner and Robert Ochsenfeld discovered the phenomenon in 1933 by measuring the magnetic field distribution outside superconducting tin and lead samples. The samples, in the presence of an applied magnetic field, were cooled below their superconducting transition temperature. Below the transition temperature the samples cancelled nearly all interior magnetic fields. They detected this effect only indirectly; because the magnetic flux is conserved by a superconductor, when the interior field decreased, the exterior field increased. The experiment demonstrated for the first time that superconductors were more than just perfect conductors and provided a uniquely defining property of the superconducting state.
The Casimir effect is a small attractive force that acts between two close parallel uncharged conducting plates.
It is due to quantum vacuum fluctuations of the electromagnetic field. The effect was predicted by the Dutch physicist Hendrick Casimir in 1948. According to the quantum theory, the vacuum contains virtual particles which are in a continuous state of fluctuation. Casimir realised that between two plates, only those virtual photons whose wavelengths fit a whole number of times into the gap should be counted when calculating the vacuum energy. The energy density decreases as the plates are moved closer, which implies that there is a small force drawing them together. Plasma actuators are a type of actuator currently being developed for aerodynamic flow control. Plasma actuators impart force in a similar way to ionocraft.
A dielectric-barrier-discharge (DBD) plasma is used to induce a flow close to a surface for flow control. The DBD plasma actuator consists of two electrodes separated by a dielectric barrier. When a high voltage alternating current is applied, the air close to the exposed electrode is ionized. On the surface the ions collide with the surrounding neutral air particles so as to transfer their momentum to the air. Therefore, the plasma actuator can be thought of as imposing a localized body force to the surrounding air. The aim of using this electric wind is in most cases to accelerate the airflow tangentially and very close to the actuator's surface in order to modify the local airflow profile. The main advantage of this process is that it directly converts electric energy into kinetic energy without involving moving mechanical parts.

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