def macs(nasv,T):
Na = avogadro_constant<EOL>k  = boltzmann_constant<EOL>vtherm=(<NUM_LIT>*k*T/mass_H_atom)**<NUM_LIT:0.5><EOL>s      = old_div(nasv,(vtherm*Na))<EOL>macs   = s*<NUM_LIT><EOL>return macs<EOL>
Returns
-------
MACS
    [mb] at T [K] from Na*<sigma v>.