Hi All,
    Found an article on Litz-wire.  On first scan it appears to give
calculations and graphs on stranding number vs gauge vs AC resistance
vs DC resistance.  It contains a 27 references to previous works on
skin-effect and eddy-current papers.

Optimal Choice for Number of Strands in a Litz-Wire Transformer
by Charles R. Sullivan
IEEE Transactions on Power Electronics, Vol. 14, No. 2, March 1999,
Pages 283 to 291