Time-dependent defects in integrable soliton equations.

We study (1 + 1)-dimensional integrable soliton equations with time-dependent defects located at x = c(t), where c(t) is a function of class C 1. We define the defect condition as a Bäcklund transformation evaluated at x = c(t) in space rather than over the full line. We show that such a defect condition does not spoil the integrability of the system. We also study soliton solutions that can meet the defect for the system. An interesting discovery is that the defect system admits peaked soliton solutions.