Xi or Csi is the 14th letter of the Greek alphabet and it has the value 60 in the Greek number system. In both ancient and modern languages, the letter is pronounced as "ksi". The csi/xi came from the Phoenician language s?mek, which meant fish. Samekh or Simketh is the 15th letter of the Phoenician alphabet. The capital letter is used in statistical mechanics and particle physics. And the lowercase xi represents the original Riemann Xi function, the damping ratio and the extent of a chemical reaction.
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