We have a combination of two very long coaxial tubes with radii R and 2R. The tubes are placed vertically, the space between the tubes is filled with a heavy fluid of viscosity. The outer tube glides stationary down under the action of gravity, the inner tube is at rest. Both tube ends are open...
I have three primitive vectors a1,a2,a3 for the body-centered cubic (bcc) Bravais can be chosen as
a1=ax
a2=ay
a3=(a/2)(x+y+z)
or, for instance, as
b1=(a/2)(y+z-x)
b2=(a/2)(z+x-y)
b3=(a/2)(x+y-z)
where x,y,z are unit vectors.
Now I should show that any vector of the form...