I found this article at
http://www.astro.cf.ac.uk/groups/relativity/papers/abstracts/miguel94a.html

Unfortunately, the postscript seemed broken so I had to reTeX it. And
I couldn't get the referred figure. Nevertheless, I found it quite
interesting.

Update, 1999-11-17:

Got the picture as well, from <URL:
http://www.astro.cf.ac.uk/pub/Miguel.Alcubierre/warp.gif>. Thanks to
Michael Soliman.

I haven't had the time to update the postscript to include the
picture, but it should be straight forward to do that starting with
warp.tex, or perhaps even warp.dvi.

/Niels Möller