Fig. 14.6. Forms with positively and negatively curved
surfaces: the sphere (top) and the outer part of a torus
(bottom left) are examples of surfaces exhibiting positive
curvatures, the saddle (bottom right) and the inner part of the
torus (bottom left) representing negative curvatures.
Fig. 14.7. Endohedral functionalization of the inner surface of
a wheel-shaped {Mo 154 } type nanocluster by cystine ligands
(polyhedral representation, carboxylate group in ball-and-stick).
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