Aging in citation networks

In many growing networks, the age of the nodes plays an important role in deciding the attachment probability of the incoming nodes. For example, in a citation network, very old papers are seldom cited while recent papers are usually cited with high frequency. We study actual citation networks to find out the distribution T(t) of t, the time interval between the published and the cited paper. For different sets of data we find a universal behaviour: T(t) t-0.9 for t tc and T(t) t-2 for t>tc where tc O(10).