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Acoustic resonances in two-dimensional radial sonic crystal shells  

Energy Technology Data Exchange (ETDEWEB)

Radial sonic crystals (RSC) are fluidlike structures infinitely periodic along the radial direction that verify the Bloch theorem and are possible only if certain specially designed acoustic metamaterials with mass density anisotropy can be engineered (see Torrent and Sanchez-Dehesa 2009 Phys. Rev. Lett. 103 064301). A comprehensive analysis of two-dimensional (2D) RSC shells is reported here. A given shell is in fact a circular slab with a central cavity. These finite crystal structures contain Fabry-Perot-like resonances and modes strongly localized at the central cavity. Semi-analytical expressions are developed to obtain the quality factors of the different resonances, their symmetry features and their excitation properties. The results reported here are completely general and can be extended to equivalent 3D spherical shells and to their photonic counterparts.

2010-07-15

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Change in runoff characteristics of alpine flowing waters caused by the use of hydroelectric power and its effects on the macro-benthos  

International Nuclear Information System (INIS)

A typical form of change in runoff characteristics caused by the widespread use of hydroelectric power in Switzerland is the intermittent draining (torrent operation). It is the aim of the present work to help elucidate possible consequences of these changes in drain onto the benthobiocoenosis. The study was carried through on the Secklisbach at Oberrickenbach (in the semicanton of Nidwalden) and one of its side streamlets (800m above sea level). The macroinvertebrate coenosis was studied at four locations with similar conditions of drainage basin, population density and topography but varying in the degree of impairment to the draining. There were monthly benthos samples taken using a Surber sampling-device. Results show that the locations not only varied in drain, but also in temperature, this being a consequence of water storage by the power plant. The readings pointed out different values for the locations in daily average temperature, day amplitudes and ...