Semiflexibility and the Persistence Length

The persistence length provides a measure of the flexibility of a polymer and is particularly useful in the case of semiflexible filaments. In the case of filaments that do not coil in solution, a measure of the end-to-end distance or the radius of gyration is not particularly useful in characterizing the molecule. The persistence length can be defined using the following formula  

using approximations for these two equations, we can write 

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