The temperature and frequency dependence of the microwave and optical conductivity are studied for a BCS superconductor with weak elastic scattering [1/r & 26(0), where r is the scattering time and b, ( T) is the BCS energy gap]. The results are interpreted in terms of a two-(luid model in which the combined oscillator strength of the 5 function at the origin and the thermally excited free-carrier conductivity is found to be only weakly temperature dependent. The low-frequency conductivity is shown to be a function of co~, in the clean limit, with a characteristic logarithmic divergence at co=0. The frequency dependence of the microwave surface resistance is discussed and comparison is made to the recent experimental results of Bonn, Hardy, and co-workers on YBa2Cu307 t; single crystals.

According to this 1-year observational study, EVAR may be a cost-effective strategy compared with OSR for high-risk patients. Longer-term data are needed to decrease the uncertainty associated with the results.

Based on commonly quoted willingness-to-pay thresholds, EVAR was not found to be cost-effective compared to OR.