Geometric model for tube categories 
Joint work with Robert Marsh (Leeds)

We describe how to construct tube categories using arcs (up to homotopy) in an annulus 
with marked points on the boundary. This allows us to compute the dimension of Ext^1 
between two indecomposable objects: It corresponds to the (signed) crossing number of the 
corresponding arcs. As a consequence, we also get the dimension of Ext^1 in the cluster tube 
as a symmetric version of this.