Rectangular to hexagonal columnar phase transition exhibited by a biforked mesogen A.C. Ribeiro, B. Heinrich, C. Cruz, H.T. Nguyen, S. Diele, M.W. Schröder and D. Guillon Eur. Phys. J. E, 10 2 (2003) 143-151 Published online: 16 April 2003 DOI: 10.1140/epje/e2003-00018-9