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Column number density is a kind of areal density, the number or count of a substance per unit area, obtained integrating volumetric number density along a vertical path: ′ =. It's related to column mass density, with the volumetric number density replaced by the volume mass density.
The Loschmidt constant or Loschmidt's number (symbol: n 0) is the number of particles (atoms or molecules) of an ideal gas per volume (the number density), and usually quoted at standard temperature and pressure. The 2018 CODATA recommended value [1] is 2.686 780 111... × 10 25 m −3 at 0 °C and 1 atm.
As there are many units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per cubic metre (kg/m 3 ) and the cgs unit of gram per cubic centimetre (g/cm 3 ) are probably the most commonly used units for density.
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.
The Avogadro constant, commonly denoted N A [1] or L, [2] is an SI defining constant with an exact value of 6.022 140 76 × 10 23 mol −1 (reciprocal moles). [3] [4] It is this defined number of constituent particles (usually molecules, atoms, ions, or ion pairs—in general, entities) per mole and used as a normalization factor in relating the amount of substance, n(X), in a sample of a ...
Density, mass per unit volume Bulk density, mass of a particulate solid or powder divided by the volume it occupies; Particle density (packed density) or true density, density of the particles that make up a particulate solid or a powder; Neutral density, mass density of seawater; Area density or surface density, mass over a (two-dimensional) area
A related intensive system parameter is the particle number density （or particle number concentration PNC), a quantity of kind volumetric number density obtained by dividing the particle number of a system by its volume. This parameter is often denoted by the lower-case letter n.
n(r, t) is the number of particles per unit volume ("number density") (SI unit: m −3); q is the charge of the individual particles with density n (SI unit: coulombs). A common approximation to the current density assumes the current simply is proportional to the electric field, as expressed by: =