Consider the annulus formed between a rod of radius �2 and a tube of radius �D. Find the velocity profile for the flow where the inner rod is rotated with speed Ω and simultaneously is pulled in the axial direction at a speed �F = �D, while the flow experiences an external constant pressure gradient of GH I applied in the direction of the rod axis. Do not assume that the gap is small compared to the radius. Effect of gravity can be neglected.

Uranium has two naturally occurring isotopes. 238u has a natural abundance of 99.3% and 235u has an abundance of 0.7%. it is the rarer 235u that is needed for nuclear reactors. the isotopes are separated by forming uranium hexafluoride uf6, which is a gas, then allowing it to diffuse through a series of porous membranes. 235uf6 has a slightly larger rms speed than 238uf6 and diffuses slightly faster. many repetitions of this procedure gradually separate the two isotopes. what is the ratio of the rms speed of 235uf6 to that of 238uf6? express your answer to five significant figures.