The principles for measuring the extinction ratio and transmittance of a polarizer are formulated by use of the principal Mueller matrix, which includes both polarization and depolarization. The extinction ratio is about half of the depolarization, and the contrast is the inverse of the extinction ratio. Errors in the extinction ratio caused by partially polarized incident light and the misalig...

The Imperfect in Romance is used in an array of constructions: progressives, habituals, generics and counterfactual conditionals. The first three all share hallmarks of the Romance Imperfect: they describe something ongoing, in the past, and which requires contextual framing. Counterfactual uses, however, do not, and thus present an important challenge for a unified semantics of the Imperfect. ...