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McCall GH 《Physical review letters》1989,62(17):1986-1988
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The boundary-value problem of the reflection and transmission of light by a composite structure, wherein a surface-relief dielectric grating is coupled to a structurally chiral volume grating, has been formulated and solved with results showing the robust co-existence of phenomena characteristic of both types of grating: namely, Rayleigh–Wood anomalies and Bragg phenomena. A mechanism to strengthen the coupling between both grating types is included – namely, a quarter wave plate – whose birefringence converts normally incident linearly polarised light at the Bragg wavelength into transmitted circularly polarised light (and vice versa). It is possible to tailor the period of the sinusoidally corrugated surface-relief grating such that the scattering of obliquely incident light from above, by the surface grating, will lead to a specific non-specular order being scattered onto a path which is normally incident on the rest of the composite structure. Significantly, such orders exhibit the circular Bragg phenomenon in reflection and transmission only if both grating types are present, making this a “truly” coupled effect. 相似文献
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Resonant ultrasound spectroscopy (RUS) is capable of determining the bulk elastic properties of a solid from its characteristic vibration frequencies, given the dimensions, density and shape of the sample. The model used for extracting values of the elastic constants assumes perfect homogeneity, which can be approximated by average-isotropic polycrystals. This approximation is excellent in the small grain regime assumed for most averaging procedures, but for real samples with indeterminate grain size distributions, it is not clear where the approximation breaks down. RUS measurements were made on pure copper samples where the grain size distribution was changed by progressive heat treatments in order to find a quantitative limit for the loss of homogeneity. It is found that when a measure of the largest grains is 15% of the sample’s smallest dimension, the deviation in RUS fits indicates elastic inhomogeneity. 相似文献
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The tendency for taxation to weaken incentives and induce inefficient behavior on the part of entrepreneurs is demonstrated with a simple example. Next the Mossin model is extended from a proportional to a progressive tax structure that closely approximates the one in place in the U.S.A. It is shown that increased progressivity causes the amount of wealth invested in the risky asset to decline rather than increase as is true with proportional taxes. 相似文献
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T.N.C. Venkatesan H.M. Gibbs S.L. McCall A. Passner A.C. Gossard W.W. Wiegman 《Optics Communications》1979,31(2):228-230
Utilizing optically induced refractive index changes, optical pulses have been shown to self sweep Fabry-Perot cavity resonances resulting in shorter pulses or abrupt self-termination. Using a glass filter of a GaAs interferometer, 150 μs and 150 ns pulses have been shortened to 10 μs and 20 ns respectively. 相似文献