Light transmission through ice and light conditions beneath ice have been investigated in the mild winter of the year 2000 in eight Estonian lakes and in one braclush water basin, Santala Bay in the Gulf of Finland. A new system designed for optical measurements beneath the ice was successfully tested. In the water body the vertical profiles of photosynthetically active radiation (PAR), temperature and oxygen were mapped. The concentrations of optically active substances (dissolved organic matter, chlorophyll a, particles) were estimated for water samples and meltwater of ice samples. The PAR band albedo was 0.28-0.76 and transmittance was 1-52% for the icelsnow cover. The light field below ice was much more diffuse than in open water conditions. Euphotic depth was 0.1-5.5 m. The amount of yellow substance in lake ice is very small in comparison with the lake water; lake ice may contain a lot of particles, but their source is atmospheric fallout rather than the water body. In some lakes a depletion of oxygen was observed. There were considerable differences between the fresh and brackish water ice (structure, stratigraphy, amount of impurities), which influenced the underwater light field.
The invention of electrospinning has solved the problem of producing micro-and nanoscaled metal oxide fibres in bulk quantities. However, until now no methods have been available for preparing a single nanofibre of a metal oxide. In this work, the direct drawing method was successfully applied to produce metal oxide (SnO 2 , TiO 2 , ZrO 2 , HfO 2 and CeO 2 ) fibres with a high aspect ratio (up to 10 000) and a diameter as small as 200 nm. The sol-gel processing includes consumption of precursors obtained from alkoxides by aqueous or non-aqueous polymerization. Shear thinning of the precursors enables pulling a material into a fibre. This rheological behaviour can be explained by sliding of particles owing to external forces. Transmission (propagation) of light along microscaled fibres and their excellent surface morphology suggest that metal oxide nanofibres can be directly drawn from sol precursors for use in integrated photonic systems.
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