ρ B  ( r , t + Δ t ) = ∫ 0 r P    ρ B     ( r ′  , t ) G s  ( r , r ′  ) 4 π r ′  2  d r ′  + ρ B ana   ( r , t + Δ t )       ( 23  )    MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=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@6E2C@