Kappa (uppercase Κ, lowercase κ or cursive ϰ; Greek: κάππα, káppa) is the 10th letter of the Greek alphabet, used to represent the /k/ sound in Ancient and Modern Greek. In the system of Greek numerals, Kʹ has a value of 20. It was derived from the Phoenician letter kaph . Letters that arose from kappa include the Roman K and Cyrillic К.
Greek proper names and placenames containing kappa are often written in English with "c" due to the Romans' transliterations into the Latin alphabet: Constantinople, Corinth, Crete. All formal modern romanizations of Greek now use the letter "k", however: Thessaloniki, Kalamata, Nikaia.
The cursive form ϰ is generally a simple font variant of lower-case kappa, but it is encoded separately in Unicode for occasions where it is used as a separate symbol in math and science. In mathematics, the kappa curve is named after this letter; the tangents of this curve were first calculated by Isaac Barrow in the 17th century.
In graph theory, the connectivity of a graph is given by κ.
In differential geometry, the curvature of a curve is given by κ.
In Cosmology, the curvature of the universe is described by κ.
In physics, the torsional constant of an oscillator is given by κ as well as Einstein's constant of gravitation.
In physics the coupling coefficient in magnetostatics is represented by κ
In fluid dynamics, the von Kármán constant is represented by κ.
In structural engineering, κ is the ratio of the smaller factored moment to the larger factored moment and is used to calculate the critical elastic moment of an unbraced steel member.
In electrical engineering, κ is the multiplication factor, a function of the R/X ratio of the equivalent power system network, which is used in calculating the peak short-circuit current of a system fault. κ is also used to notate conductivity, the reciprocal of resistivity, rho.
In Thermodynamics, the compressibility of a compound is given by κ.
In psychology and psychiatry, kappa represents a measure of diagnostic reliability.
In biology, kappa and kappa prime are important nucleotide motifs for a tertiary interaction of group II introns.
In biology, kappa designates a subtype of an antibody component.
In pharmacology, kappa represents a type of opioid receptor.
Kappa statistics such as Cohen's kappa and Fleiss' kappa are methods for calculating inter-rater reliability.
Upper-case letter Κ is used as a symbol for:
In textual criticism, the Byzantine text-type (from Κοινη, Koine, the common text).
In set theory, kappa is often used to denote an ordinal that is also a cardinal.
In Chemistry, kappa is used to denote the denticity of the compound.
Mathematical Kappa
These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style.
