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
Prefix code prefix code. As with a prefix code, the representation of a string as a concatenation of such words is unique. A bifix code is a set of words which is both a prefix and a suffix code. An optimal prefix code is a prefix code with minimal average length. That is, assume an alphabet of symbols with probabilities formula_2 for a prefix code . If is another prefix code and formula_3 are the lengths of the codewords of , then formula_4. Examples of prefix codes include: Commonly used techniques for constructing prefix codes include Huffman codes and the earlier Shannon-Fano