Fig. 5

Knowledge diaspora between areas. a If an author publishes in different topics at time τ and at time τ+Δ τ, we count one transition between all combinations of topics; b if an author publishes in topics A and B at time τ, and at time τ+Δ τ again in topic A but not in B anymore, then we consider just one self-transition from topic A to itself; c consistently, if an author publishes in topics A and B both at time τ and at time τ+Δ τ, we only count two self-transitions; d more generally, if an author publishes in different topics at time τ, and one of them (C) disappears at time τ+Δ τ, whereas another (D) appears, since we can not know from with topic at time τ there is a transition to topic D at time τ+Δ τ, we therefore invoke the “Ceteris paribus” principle, suggesting that we have to count one transition from any topic at time τ to topic D