NMR Velocity Imaging of Fano Flow

Now let us take a look at a recent NMR imaging experiment of Fano flow, in which the local velocities in the tubeless column were mapped out quantitatively and nondestructively [20], For such a set-up, the weight force of the column is balanced by the extensional stress difference azz - axx associated with the vertical velocity gradient (dvz/dz), as 

Fano columns are most easily formed in viscoelastic solutions where extensional viscosities exceed shear viscosities by several orders of magnitude. 

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