1. S. Chandrasekhar:Liquid Crystals (Cambridge, 1977 ), p. 98.
2. P. G. De Gennes:The Physics of Liquid Crystals (Oxford, 1974), p. 77.
3. D. W. Berreman:Phys. Rev. Lett.,28, 1683 (1972).
4. E. Guyon, P. Pieranski andM. Boix:Lett. Appl. Eng. Sci.,l, 19 (1973).
5. E. Guyon, W. Urbach andM. Boix:Appl. Phys. Lett.,25, 479 (1974).