The unramified Brauer group of norm one tori
  Let k be a number field and K/k Galois. We transform the construction of the unramified Brauer group of the norm one torus R^1_K/k(G_m) into the construction of a special abelian extension over K. If k=Q and K/Q biquadratic, we explicitly construct the unramified Brauer group of R^1_K/Q(G_m). 
Dasheng Wei
math.NT