Russian doll model

An important question relating to the structure of nanotubes is Are nanotubes made of embedded closed tubes, like "Russian dolls," or are they composed of a single graphene layer which is spirally wound, like a roll of paper Ijima et al. [2] espouse the "Russian doll" model based on TEM work which shows that the same number of sheets appear on each side of the central channel. Dravid et al. [4], however, support a "paper roll" structural model for nanotubes. 

Figure 8-59. Idealized models of multi-wall nanotubes (a) Russian doll (b) hexagonal prism (e) scroll.

The representation of molecular structure can be looked upon as a hierarchical process similar to the Russian doll, which contains a series of dolls hidden inside it. At the very elementary level, the structure of the model of an assembled entity, e.g., a molecule comprising atoms, can be represented by a graph G = (V, E), where y represents a non-empty set and is a binary relation defined on the set V. When V represents a set of atoms and E symbolizes the set of covalent (or any other) bonds, we have the simplest representation of molecular structure [13,18]. Invariants derived from such graphs or matrices derived from them are the simplest structural descriptors of molecules. 

In the final analysis in the structure of most hydrogeochemical models are identified the following groups of mutually associated parameters, which form three submodels, inserted into one another as in Russian nesting dolls ... 

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