1. F. M. Mazzolai, P. G. Bordoni andF. A. Lewis:J. Phys. F,10 (1980), 78111, 337 (1981).
2. M. H. Protter andH. F. Weinberger:Maximum Principles in Differential Equations (Prentice Hall Inc., Englewood Cliffs, N.Y., 1967), p. 160.
3. E. Jahnke andF. Emde:Tables of Functions, 4th edition (Dover Publication, New York, N.Y., 1945), p. 272.
4. See the result quoted in note —.
5. A. J. Maeland andT. E. Flanagan:J. Chem. Phys.,68, 1419 (1964);D. K. Hsu andR. C. Leisure: Phys. Rev. B,20, 1939 (1979).