The Greek letter **τ** (tau) was derived from the ancient Phoenician letter 𐤕 (tāw) which, in turn, was derived from an Egyptian hieroglyph **✕** meaning “mark”.

The lower-case τ has many uses in maths, engineering and sciences, such as:

- in biochemistry: the τ protein, a protein that stabilise microtubules
- in continuum mechanics: shear stress
- in differential geometry: torsion of a curve
- in engineering and physics: the time constant of a system
- in geometry: the tortuosity
- in mathematics: the Ramanujan tau function, an irrational number with approximate value of 0.41468
- in mechanics: the torque, aka moment of force
- in optics: optical depth of a material, defined as
*τ*= −ln*T*, where*T*is the transmittance of that material - in particle physics: tauon τ
^{−}and antitauon τ^{+} - in physical sciences: relaxation time
- in physics: the lifetime of a spontaneous emission process
- in relativity: proper time
- in spectroscopy: rotational correlation time
- in statistics: the Kendall rank correlation coefficient

## No comments:

## Post a Comment