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Density (volumetric mass density or specific mass) is a substance's mass per unit of volume. The symbol most often used for density is ρ (the lower case Greek letter rho ), although the Latin letter D can also be used.
In materials science, bulk density, also called apparent density, is a material property defined as the mass of the many particles of the material divided by the bulk volume. Bulk volume is defined as the total volume the particles occupy, including particle's own volume, inter-particle void volume, and the particles' internal pore volume.
The density matrix is a representation of a linear operator called the density operator. The density matrix is obtained from the density operator by a choice of an orthonormal basis in the underlying space. [2] In practice, the terms density matrix and density operator are often used interchangeably.
The density of air or atmospheric density, denoted ρ, [1] is the mass per unit volume of Earth's atmosphere. Air density, like air pressure, decreases with increasing altitude. Air density, like air pressure, decreases with increasing altitude.
Population density (people per km 2) by country. This is a list of countries and dependencies ranked by population density, sorted by inhabitants per square kilometre or square mile. The list includes sovereign states and self-governing dependent territories based upon the ISO standard ISO 3166-1.
A subset A of positive integers has natural density α if the proportion of elements of A among all natural numbers from 1 to n converges to α as n tends to infinity.. More explicitly, if one defines for any natural number n the counting function a(n) as the number of elements of A less than or equal to n, then the natural density of A being α exactly means that [1]
Relative density, also called specific gravity, [1] [2] is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material.
The area density (also known as areal density, surface density, superficial density, areic density, mass thickness, column density, or density thickness) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is the "kilogram per square metre" (kg·m −2).