An explanation is given of the low value of Rλ ≡ Aλ/E(B − V ), the ratio of absolute to selective extinction deduced from Type Ia supernova observations. The idea involves scattering by dust clouds located in the circumstellar environment, or at the highest velocity shells of the supernova ejecta. The scattered light tends to reduce the effective Rλ in the optical, but has an opposite effect in...

about 35 samples were collected from lower and upper parts of the proposed frasnianamennian boundary in three sections of upper devonian marine sediments of the kerman province. the biostratigraphical and geochemical studies indicate that about 45% extinction of brachiopods probably caused by the frasnian-famennian bioevents, which is slightly higher than thr rate of devonian-carboniferous exti...

Calculations of the extinction and polarization profiles in the wavelength range λλ 2.7–22 µm have been performed for silicate core – icy mantle spheroidal grains using the exact solution to the light scattering problem and the Rayleigh approximation. It is concluded that the 10% accuracy of the Rayleigh approximation is guaranteed in the case of extinction (polarization) if the particle size d...

Enhancing the optical cross section is an enticing goal in light-matter interactions, due to its fundamental role in quantum and nonlinear optics. Here, we show how dipolar interactions can suppress off-axis scattering in a two-dimensional atomic array, leading to a subradiant collective mode where the optical cross section is enhanced by almost an order of magnitude. As a consequence, it is po...

The relationship between light extinction coefficient (kT) and Secchi depth (ZSD), as well as that between these variables and chlorophyll-a concentration (chl-a) and suspended material (SST) was studied in the Sau reservoir between 1995 and 2001. The results show that kT and ZSD are correlated by the equation kT = 1.36 ZSD, although this relationship exhibits a high inter-annual variability. A...