Effect of the age of papers on the preferential attachment in citation networks

In this paper, we investigated the influences of the age of papers on the preferential attachment on the basis of three actual citation networks. We found that the time dependence of the attachment rate Π (k, t) follows a uniform exponentially decreasing function, T (t) ∼ exp (- λ t), in different citation networks. Younger papers are more likely to be cited by new ones than older papers. On the basis of the aging influences, we modified the expression for the preferential attachment, to Π (k, t) ∝ k * exp (- λ t). Our results show that the modified preferential attachment works well for citation networks.