Doppler boosting and de-boosting effects in relativistic jets of AGNs and GRBs

It is widely accepted that the Doppler de-boosting effects exist in counter relativistic jets. However, people often neglect another important fact that both Doppler boosting and de-boosting effects could happen in forward relativistic jets. Such effects might be used to explain some strange phenomena, such as the invisible gaps between the inner and outer jets of AGNs, and the rapid initial decays and re-brightening bumps in the light curves of GRBs.