||Neil R. Voss. 2006 'Geometric Studies of RNA and Ribosomes, and Ribosome Crystallization' Table 3.4 pp. 97 link - link
||Edayathumangalam et al 2004. PDB entry 1s32
||a computer program that uses the rolling probe algorithm to obtain a shell. The algorithm can generate an infinite number of surfaces for a macromolecule simply by varying the radius of probe used.
||The “shell” of a macromolecule is the limiting surface used to distinguish the interior of the macromolecule from its exterior. The shell volume is the volume inside that surface. for further definition see section 3.2.2 page 52 of ref link - link