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The ecological success of diatoms is emphasized by regular blooms of many different species in all aquatic systems, but the reason behind their success is not fully understood. A special feature of the diatom cell is the frustule, a nano-patterned cell encasement made of amorphous biosilica. The optical properties of a cleaned single valve (one half of a frustule) from the diatom Coscinodiscus centralis were studied using confocal micro-spectroscopy. A photonic crystal function in the frustule was observed, and analysis of the hyperspectral mapping revealed an enhancement of transmitted light around 636 and 663 nm. These wavelengths match the absorption maxima of chlorophyll a and c, respectively. Additionally, we demonstrate that a highly efficient light trapping mechanism occurred, resulting from strong asymmetry between the cribrum and foramen pseudo-periodic structures. This effect may prevent transmitted light from being backscattered and in turn enhance the light absorption. Based on our results, we hypothesize that the multi-scaled layered structure of the frustule improves photosynthetic efficiency by these three mechanisms. The optical properties of the frustule described here may contribute to the ecological success of diatoms in both lentic and marine ecosystems, and should be studies further in vivo.

The redox behavior of titanium in CaO-SiO 2 -TiO x melts was investigated using a slag-gas equilibrium technique. Titanium partitioning between Ti 3+ and Ti 4+ valency states and the ratio of activity coefficients of TiO 1.5 and TiO 2 were determined as functions of oxygen partial pressure, temperature, and slag composition. The equilibrium experiments were carried out at temperatures between 1783 and 1903 K under CO-CO 2 -Ar gas atmosphere with oxygen partial pressure ranging from 10 Ϫ12 to 10 Ϫ7 atm (1.01 ϫ 10 Ϫ10 kPa to 1.01 ϫ 10 Ϫ5 kPa). The slags had CaO/SiO 2 ratios between 0.55 and 1.35 and total titanium oxide concentrations from 7 to 50 mass pct. Experimental results showed that the Ti 3+ /Ti 4+ ratio in CaO-SiO 2 -TiO x slags, containing up to 50 mass pct TiO x , increased with decreasing oxygen partial pressure and decreased with increasing CaO/SiO 2 ratio and decreasing temperature. Measured variation of the redox ratio Ti 3+ /Ti 4+ with oxygen partial pressure closely followed the ideal behavior. Increasing the CaO/SiO 2 ratio increased the ratio of activity coefficients of TiO 1.5 and TiO 2 . The effect of total titania content on this ratio was more complex and in accord with Raman spectroscopy data.

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