One might speculate that λ c would be on the order of the dimensions of the pore. Letting D = 6 √ 2σ co 2 , one finds that for λ c = 2R o , Eq. ( ) yields approximately 15.0 bar while for λ c = 4R o , P m ≈ 7.5 bar. Therefore, the gas at the point of spilling out of the layer is beyond the rarefied range. This leads us to speculate that highly rarefied gases will remain securely within the outer layer in such a nanotube.