Linguistic validation into 20 languages and content validity of the rheumatoid arthritis-specific Work Productivity and Activity Impairment questionnaire.

Background: Impairments in work productivity and daily activities contribute to the burden of rheumatoid arthritis (RA). It is thus essential to use an instrument assessing both work and daily activity impairments when studying the full impact of RA on individuals. The Work Productivity and Activity Impairment (WPAI) questionnaire is such an instrument.

Localization of harmonics generated in nonlinear shallow water waves.

The propagation of nonlinear shallow water waves over a random seabed is studied. A bathymetry which fluctuates randomly from a constant mean adds multiple scattering to resonant interactions and harmonic generation. By the method of multiple scales, nonlinear evolution equations for the harmonic amplitudes are derived.