144
R. Zhang et al.
Uptrend
Downtrend
Critical frequency
Fig. 5. The opening degree is 15°
Critical frequency
Uptrend
Downtrend
Fig. 6. The opening degree is 20°
Critical frequency
Uptrend
Downtrend
Fig. 7. The opening degree is 25°
Critical frequency
Uptrend
Downtrend
Fig. 8. The opening is 30°
Critical frequency
Uptrend
Downtrend
Fig. 9. The opening degree is 35°
Critical frequency
Uptrend
Downtrend
Fig. 10. The opening degree is 40°