In spite of its almost photographic realism, the Arnolfi ni Portrait by naturalistic painter Jan van Eyck exhibits faulty linear perspective. This paper describes the creation of a three-dimensional virtual reconstruction of the painting’s interior scene using commercial modelling and image processing software. The result presented here is a rendering of the reconstructed scene closely resembli...

We discuss “spectral flow” coordinate transformations that take asymptotically fourdimensional solutions into other asymptotically four-dimensional solutions. We find that spectral flow can relate smooth three-charge solutions with a multi-center Taub-NUT base to solutions where one or several Taub-NUT centers are replaced by two-charge supertubes, and vice versa. We further show that multi-par...

The asymptotic behavior of Einstein-Rosen waves at null infinity in 4 dimensions is investigated in all directions by exploiting the relation between the 4-dimensional space-time and the 3-dimensional symmetry reduction thereof. Somewhat surprisingly, the behavior in a generic direction is better than that in directions orthogonal to the symmetry axis. The geometric origin of this difference ca...

We study rational streams (over a field) from a coalgebraic perspective. Exploiting the finality of the set of streams, we present an elementary and uniform proof of the equivalence of four notions of representability of rational streams: by finite dimensional linear systems; by finite stream circuits; by finite weighted stream automata; and by finite dimensional subsystems of the set of streams.