Crossover from conserving to lossy transport in circular random-matrix ensembles

In a quantum dot with three leads, the transmission matrix t(12) between two of these leads is a truncation of a unitary scattering matrix S, which we treat as random. As the number of channels in the third lead is increased, the constraints from the symmetry of S become less stringent and t(12) becomes closer to a matrix of complex Gaussian random numbers with no constraints. We consider the distribution of the singular values of t(12), which is related to a number of physical quantities.