This condition will clearly be fulfilled if the average distance, dtravel, travelled by an entity during the time interval Δt is less than the average distance between particles, d. The average travel distance is: dtravel = dtravel=6DΔt MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=vr0dc8meaabaqaciaacaGaaeqabaqabeGadaaakeaacqWGKbazdaWgaaWcbaGaeeiDaqNaeeOCaiNaeeyyaeMaeeODayNaeeyzauMaeeiBaWgabeaakiabg2da9maakaaabaGaeGOnayJaemiraqKaeuiLdqKaemiDaqhaleqaaaaa@3C7C@, where D is the diffusion constant. The average interparticle distance given by: d=(VN)1/3 MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=vr0dc8meaabaqaciaacaGaaeqabaqabeGadaaakeaacqWGKbazcqGH9aqpcqGGOaakdaWcaaqaaiabdAfawbqaaiabd6eaobaacqGGPaqkdaahaaWcbeqaaiabigdaXiabc+caViabiodaZaaaaaa@3616@, where V is the volume and N is the number of particle, can also be expressed in terms of the concentration as: d ∝ C-1/3. where C is the concentration. For typical biological situations, C ≃ μM ml-1 and D ≃ μm2s-1, such that the condition reduces to Δt <~0.002 s.