Several people have reported problems with the domain name
diffusiondemo.org sometimes not resolving properly.  It redirects to
this page at the Indiana Supercomputing Center:

https://diffusion-demo.cis240773.projects.jetstream-cloud.org/

Feel free to use this direct link if diffusiondemo.org is not
resolving for you.  We're sorry for the inconvenience.

-- Dave Touretzky