US. Patent Oct. 21, 2008 Sheet 1 of8 US 7,438,681 B2 “\ I 20 43 47 57 25 49 30 45 \ 48 U u , , 40 98 . 70 \ 85 86 6° Figure 2a 35 A 98 /— 41 57 — > Figure 2b V 50 60 Figure 1 Figure 2c Figure 2d