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
English prefix particular lexical categories (or "parts of speech"). For example, the prefix "re-" meaning "again, back" is only added to verb bases as in "rebuild", "reclaim", "reuse", "resell", "re-evaluate", "resettle". It cannot be added to bases of other lexical categories. Thus, examples of "re-" plus a noun base (such as the ungrammatical "*rehusband", "*remonopoly") or "re-" plus an adjective base ("*renatural", "*rewise") are virtually unattested. These selectional restrictions on what base a prefix can be attached to can be used to distinguish between otherwise identical-sounding prefixes. For instance, there are two different "un-" prefixes in English: one meaning "not, opposite of",