Cryogenics Cryogenics In physics, cryogenics is the production and behaviour of materials at very low temperatures. A person who studies elements that have been subjected to extremely cold temperatures is called a "cryogenicist". It is not well-defined at what point on the temperature scale refrigeration ends and cryogenics begins, but scientists assume a gas to be cryogenic if it can be liquefied at or below . The U.S. National Institute of Standards and Technology has chosen to consider the field of cryogenics as that involving temperatures below . This is a logical dividing line, since the normal boiling points of the
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",