1. Bersanelli, M. 1996.COBRAS/SAMBA, A Mission Dedicated to Imaging the Anisotropies of Anisotropies of the Microwave Background, Preprint ESA D/SCI(96)3.
2. Chepurnov, A. V. 1995. Preprint SAO RAS No. 107SPb (in Russian).
3. The galactic distribution of free electrons
4. Davies, R. D., Watson, R. A. and Gutierres, C. M. 1995. Jodrell Bank Preprint No. 1215.