High-resolution birefringence study at the nematic-smectic A phase transition of ZnS nano particle dispersed octyloxycyanobiphenylMalay Kumar Das, Purna Chandra Barman and Sudipta Kumar SarkarEur. Phys. J. B, 88 7 (2015) 175DOI: https://doi.org/10.1140/epjb/e2015-60202-7