For a long chain of spheres, the outer contribution acts only at
the ends of the chain while the inner one acts at every gap between
spheres. Hence, for long chain of spheres, the most contributive
component is expected to be the inner contribution and outer
contribution will be neglected below; i.e. the SD deformation
SSD ¼ Sinner. In Fig. 4, the curve of SSD versus a/D is plotted.