1. D. Vautherin, Lectures given at Yukawa Institute, Kyoto, 1995, (unpublished).
2. A. A. Anselm and M.G. Ryskin, Phys. Lett. B266, 482 (1991).
3. J.-P. Blaizot and A. Krzywicki, Phys. Rev. D 46, 246 (1992).
4. K. Rajagopal and F. Wilczek, Nucl. Phys. B404, 577 (1993).
5. A. Guth and S. Y. Pi, Phys. Rev. D32, 1899 (1985).