This paper has now appeared as

but was held here.


Legal Note

We, as administrator's of this service do so in order to promote the efficient dissemination of information between academic institutions, to promote research in the area of MCMC methodology.

It is common academic practice to assign the copyright of published papers to the publisher when the paper appears. Thus, the provision, distribution or downloading of copyright material may infringe the publisher's copyright and anyone distributing or downloading copyright material must seek permission from the copyright holder before doing so.

The adminstrator's of this service, the School of Mathematics and the University of Bristol accept no liability in respect of copyright infringement by users of this service.