content_image/370993.jpg
<img src='content_image/370993.jpg'>

changing the double-walled carbon nanotube considered. 

Keeping the same α value of the 7 K/nm case and using γ = 0.5 pN ps $^{2}$/ ˚ A $^{2}$, we can see in Figure S7 that the steady velocity state will be achieved for even longer outer tubes for a thermal gradient of 0.1 K/nm. Thus, the value of 1 µ m for the outer tube length can be considered as a lower limit where stead velocity state is expected, for thermal gradients below ∼ 10 K/nm. 

