Howitzer groups called batteries. The English word ""howitzer"" comes from the Czech word ""houfnice"", from "houf", "crowd", and "houf" is in turn a borrowing from the Middle High German word "Hūfe" or "Houfe" (modern German "Haufen"), meaning "heap". "Haufen", sometimes in the compound "Gewalthaufen", also designated a pike square formation in German. In the Hussite Wars of the 1420s and 1430s, the Czechs used short barreled ""houfnice"" cannons to fire at short distances into crowds of infantry, or into charging heavy cavalry, to make horses shy away. The word was rendered into German as "aufeniz" in the earliest attested use in
Field emission gun Field emission gun A field emission gun is a type of electron gun in which a sharply pointed Müller-type emitter is held at several kilovolts negative potential relative to a nearby electrode, so that there is sufficient potential gradient at the emitter surface to cause field electron emission. Emitters are either of cold-cathode type, usually made of single crystal tungsten sharpened to a tip radius of about 100 nm, or of the Schottky type, in which thermionic emission is enhanced by barrier lowering in the presence of a high electric field. Schottky emitters are made by coating a tungsten tip