  The precise calculations are carried out on the flavor changing neutral
current couplings in the process $pp \to gg \to t\bar{c}(\bar{t}c)$ at the
large hadron collider(LHC) and very large hadron collider(VLHC) in both
frameworks of the minimal standard model(MSM) and its extension with extra
dimensions. We find that the effects from the large extra dimensions can
enhance the total cross section up to about several hundred times as that in
the MSM, quantitatively.
