Waves in periodically structured media

Waves in structured media: non-radial solar p modes

For non-radial solar p modes we calculate corrections to the eigenfrequencies arising from the sound speed and velocity inhomogeneity of the convection zone. We use a simple periodic model, and obtain the frequency corrections by solving a Hill determinant. The frequency shifts are significant, and in most cases negative; they increase in magnitude with increasing frequency and harmonic degree ...

Asymptotic analysis of periodically-perforated nonlinear media

A well-known result on the asymptotic behaviour of Dirichlet problems in perforated domains shows the appearance of a ‘strange’ extra term as the period of the perforation tends to 0. In a paper by Cioranescu and Murat [10] (see also e.g. earlier work by Marchenko Khrushlov [17]) the following result (among others) is proved. Let Ω be a bounded open set in R, n ≥ 3 and for all δ > 0 let Ωδ be t...

A technique for perceptually reducing periodically structured noise in speech

Periodically structured noise is noise which occurs randomly but with a fixed or slowly varying period. The noise periodicity is usually due to some underlying process, such as block processing of the speech where discontinuities between successive blocks result. This type of noise permeates the entire speech spectrum and is not removable by standard filtering techniques. The recently developed...

Modulated waves in a periodically driven annular cavity

Time-periodic flows with spatio-temporal symmetry Z2 × O(2) – invariance in the spanwise direction generating the O(2) symmetry group and a half-period-reflection symmetry in the streamwise direction generating a spatio-temporal Z2 symmetry group – are of interest largely because this is the symmetry group of periodic laminar two-dimensional wakes of symmetric bodies. Such flows are the base st...

Nonlinear Waves in Transmission Lines Periodically Loaded with Tunneling Diodes