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Air transparent soundproof window
A soundproof window or wall which is transparent to airflow is presented. The
design is based on two wave theories of diffraction and acoustic metamaterials.
It consists of a three-dimensional array of strong diffraction-type resonators
with many holes centered at each individual resonator. The acoustic performance
levels of two soundproof windows with air holes of and diameters
were measured. Sound waves of 80dB in the frequency range of
were applied to the windows. It was observed that the sound level was reduced
by about dB in the above frequency range with the window and by
about dB in the frequency range of with the
window.
It is an extraordinary acoustic anti-transmission. The geometric factors
which produced the effective negative modulus were obtained.Comment: 4 pages, 6 figures, 1 tabl
Quartically hyponormal weighted shifts need not be 3-hyponormal
We give the first example of a quartically hyponormal unilateral weighted
shift which is not 3-hyponormal
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