. "Number of Particles"@en . . "N_B" . . "http://en.wikipedia.org/wiki/Particle_number"^^ . "http://www.iso.org/iso/catalogue_detail?csnumber=31894"^^ . "\"Number of Particles\", also known as the particle number, of a thermodynamic system, conventionally indicated with the letter N, is the number of constituent particles in that system." . .