    ![The time dependence of the system density $\rho$ (a) and the density auto-correlation functions $C_\rho(t)$ (b) for the systems with various angles between nanotube axes $\varphi$. The dots correspond to the calculated data. The solid lines correspond to the fitting of $C_\rho(t)$ with the exponential (in case of $\varphi=0^\circ$) or double exponential (in case of of $\varphi=00^\circ$ and $\varphi=00^\circ$) functions.[]{data-label="fig_Larin-density"}](figs/fig_Larin_dens/fig_