Figure 4: Comparison between four-link ‘T-swimmer’ and swimming S. mansoni cercariae. | Nature Physics

Figure 4: Comparison between four-link ‘T-swimmer’ and swimming S. mansoni cercariae.

From: Schistosoma mansoni cercariae swim efficiently by exploiting an elastohydrodynamic coupling

Figure 4

a, Schematic of a four-link swimmer model overlayed on an image of a cercariae. The flexibility at the tail–fork and tail–body joints in cercariae is modelled via linear torsional springs, depicted as black spirals at the respective joints. b, Free body diagrams of the body and fork, showing translational and angular velocities and the resulting hydrodynamic torque about the respective joints. This torque is balanced instantaneously by the mechanical torques at the joints, thus allowing in situ means of estimating these torques (Supplementary Methods and Supplementary Section 2.3). Scale bar, 100 μm. c, Plot of the estimated torques (normalized by μflc3) at the tail–body (blue triangles) and tail–fork (red circles) joints as a function of the corresponding joint angles φtb and φtf (over five swimming cycles). The slope of the respective linear fits (R-squared tail–body 0.7 and tail–fork 0.8) shown as solid blue and dashed red lines gives the joint stiffnesses (Γtb and Γtf) in live, swimming cercariae. d, Time series plot of displacements (normalized by lc) of the body along ŝ and for the four-link T-swimmer with estimated joint stiffnesses (black solid and dashed curves) compared with experimental measurements (red circles and green triangles). e, Phase plot between φtb, φtf and φt for the four-link T-swimmer, shown as blue and red lines, and for cercariae shown as blue triangles and red circles. f,g, Contour plots of average swimming speed (normalized by flc) (f) and swimming efficiency (g) as a function of the joint stiffnesses Γtf and Γtb show a single optimal point (black crosses). The red dots indicate the values estimated for cercariae, showing that they optimize their joint stiffnesses to swim efficiently.

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