Cryogenics scale, both of which measure from absolute zero, rather than more usual scales such as Celsius or Fahrenheit, with their zeroes at arbitrary temperatures. The word "cryogenics" stems from Greek "κρύο (cryo)" – "cold" + "γονική (genic)" – "having to do with production". Cryogenic fluids with their boiling point in Kelvin Liquefied gases, such as liquid nitrogen and liquid helium, are used in many cryogenic applications. Liquid nitrogen is the most commonly used element in cryogenics and is legally purchasable around the world. Liquid helium is also commonly used and allows for the lowest attainable temperatures to be reached. These
Prefix order Prefix order In mathematics, especially order theory, a prefix ordered set generalizes the intuitive concept of a tree by introducing the possibility of continuous progress and continuous branching. Natural prefix orders often occur when considering dynamical systems as a set of functions from "time" (a totally ordered set) to some phase space. In this case, the elements of the set are usually referred to as "executions" of the system. The name "prefix order" stems from the prefix order on words, which is a special kind of substring relation and, because of its discrete character, a tree. A prefix order is