Silica bulk losses are unreferenced
In the aLIGO and A+ yaml files, a model for bulk silica loss is given as follows:
c2 : 7.6e-12 # Coeff of freq depend. term for bulk mechanical loss, 7.15e-12 for Sup2
MechanicalLossExponent: 0.77 # Exponent for freq dependence of silica loss, 0.822 for Sup2
Where do these numbers come from?