Radio atmospheric km. For ELF waves (< 3 kHz), ray theory becomes invalid, and only mode theory is appropriate. Here, the zeroth mode begins to dominate and is responsible for the second window at greater distances. Resonant waves of this zeroth mode can be excited in the Earth–ionosphere waveguide cavity, mainly by the continuing current components of lightning flowing between two return strokes. Their wavelengths are integral fractions of the Earth's circumference, and their resonance frequencies can thus be approximately determined by "f" ≃ "mc"/(2π"a") ≃ 7.5 "m" Hz (with "m" = 1, 2, ...; "a" the Earth's radius and "c" the
Atmospheric-pressure plasma to coat varied surfaces by means of this technique. Thus, anticorrosive layers and adhesion promoter layers can be applied to many metals without the use of solvents and hence in an environmentally friendly manner. Atmospheric-pressure plasma Atmospheric-pressure plasma (or AP plasma or normal pressure plasma) is a plasma in which the pressure approximately matches that of the surrounding atmosphere – the so-called normal pressure. Atmospheric-pressure plasmas have prominent technical significance because in contrast with low-pressure plasma or high-pressure plasma no reaction vessel is needed to ensure the maintenance of a pressure level differing from atmospheric pressure. Accordingly, depending on the