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 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