ERRATA

1. At the end of equation (11), please add the expression: - 4π(z-z₀+|z-z₀|)/A J

2. First fraction on the right-hand side of (54): please replace ``b<sup>2</sup>'' with ``π b²''
   The fraction itself represents the number density of the circular perforations.

3. Second fraction in (55): please replace ``3'' with ``3 π''
4. Third fraction in (55): please replace ``9'' with ``9 π''
5. Fourth fraction in (55): please replace ``4π'' with ``4''
6. Second fraction in (56): please replace ``9'' with ``9 π''