Acknowledgements

The work of AM and RJP is supported by the Australian Research Council. RE and TS acknowledge the support by the U.S. Department of Energy under Grant Number DE FG02 01 ER 40626. The work of TS is also supported in part by NASA NAG5-7009. The work of JPR is supported by NASA NAG5-2857. TS thanks the University of Adelaide for hospitality during his visit, which was funded in part by the International Visitor Program of the Special Research Center for Theoretical Astrophysics, University of Sydney, when this work was started. We acknowledge a helpful discussion with Eli Waxman and Venya Berezinsky.

© Copyright Astronomical Society of Australia 1997