Figure 3

Lack of knowledge flows. An example of several validated pairs of articles in the APS citation network at \(p^{*}=10^{-7}\). Articles are reported in order of publication time, from older (left) to more recent (right) ones. The occurrence of a link indicates that the pair of articles has passed the statistical test, while the colour of the link indicates that the most recent article in the pair actually did (green) or did not (red) cite the other one. In this case, all the articles represented as yellow nodes are articles co-authored by researchers in the same group, while article A was co-authored by another group. The identification of a large number of missing citations suggests that the two groups might have been unaware of the work of their colleagues in the same field.