- Psi (letter)
:"For other uses, see
Psi."Psi (uppercase Ψ, lowercase ψ) is the 23rd letter of the Greek alphabetand has a numeric value of 700. In both Classical and Modern Greek, the letter indicates the combination /ps/ (like in English "lapse"). In Greek, this consonant cluster can occur in the syllable initial position, as in the Greek word "ψάρι" [psári (=fish)] . However, in some languages (including English) this combination is not possible at the beginning of a syllable. In Latin, Greek words beginning with psi are transcribed by "ps-", but seem to have been pronounced simply as "s-", with a quiescent "p".Fact|date=May 2007 This pronunciation has affected that of Greek loanwords beginning with the letter in several languages. In English, for example, "psychology" is pronounced with a silent "p", and the name of the letter is often pronounced IPA| [saɪ] ("sigh"), although this is not always the case. The letter was adopted into the Old Italic alphabet, and its shape is continued into the Algizrune of the Elder Futhark.
The letter may have originated from the practice of writing the
sigmaover the pi, eventually making the combination into a single letter.Fact|date=November 2007 Psi was also adopted into the early Cyrillic alphabet. See psi (Cyrillic)(Unicode|Ѱ, Unicode|ѱ). This may have also been since the letter, both in lower case and uppercase form, resembles the tridentwielded by Poseidon, the Greek god of water/ocean.
The letter psi is commonly used in
physicsfor representing a wavefunctionin quantum mechanics, particularly with the Schrödinger equationand bra-ket notation: . It is also used to represent the (generalized) positional states of a qubitin a quantum computer.
Psi is also used as the symbol for the
polygamma function, defined by:where is the gamma function.
The letters Ψ or ψ can also be a symbol for:
psychology, psychiatry, and sometimes parapsychology(involving paranormalor relating with the supernaturalsubjects).
*In mathematics, the number of the "Supergolden Ratio", approximately 1.4 and the solution to the cubic equation x³ = x² + 1.
Water potentialin movement of water between plant cells.
Stream functionin fluid mechanicsdefining the curve to which the flow velocityis always tangent.
*One of the
dihedral angles in the backbones of proteins
Schrodinger Equationand throughout quantum mechanics, ψ(x) stands for the wave function
Indiana University(as a superimposed Iand U)
*A Sai, the name of which is pronounced the same way.
Pharmacology, general pharmacy
virologythe ψ site is a viral packaging signal.
J/ψmeson, in particle physics.
*In the manga
Monochrome, Psi is a mentally disturbed character, though her name is usually spelled out.
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