Helical filaments with varying cross section radius

The tridimensional configuration and the twist density of helical rods with varying cross section radius are studied within the framework of the Kirchhoff rod model. It is shown that the twist density increases when the cross section radius decreases. Some tridimensional configurations of helix-like rods are displayed showing the effects of the nonhomogeneity considered here. Since the helix-like solutions of the nonhomogeneous rods do not present constant curvature and torsion a set of differential equations for these quantities is presented. We discuss the results and possible consequences.