Diatoms generate their cell walls by silica biomineralization. The cell walls are composed of silica and organic macromolecules and show a complex microscopic structure. Analysis of this structure by different atomic force microscopy (AFM) techniques revealed an unexpected nanostructured granular surface. Silaffins, proteins that are posttranslationally modified with long-chain polyamines, and oligo-N-methylpropyleneamines were identified as the main organic constituents of diatom biosilica. 1 Silaffins as well as free propyleneamines of different chain lengths induce rapid precipitation of nanosized particles from silicic acid solutions in vitro. In a biomimetic approach, we reacted aqueous silicic acid solution with tripropylenetetramine in CHCl 3 in a biphasic system. As a result, thin nanostructured silica layers that show a granular nanostructure very similar to that of the diatom cell walls were obtained. This finding may serve as a good model to study the mechanisms that lead to the nanostructure of the diatom cell walls.

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Oxygen content and oxide kinetics determine response time Diffusion profiles have been recorded in situ and evaluated in bulk conductivity sensors, drift effects in surface conductivusing an optical technique. In this way, bulk diffusion coefity sensors, speed of oxygen permeation in chemical filters, ficients have been reliably and quantitatively measured. It performance of oxide electrodes, lifetime in some perovskite is shown that the values agree with calculations without capacitor materials stressed by applied voltage, annealing temusing adjustable parameters if the coupling of the diffusperature in high-temperature superconductors, 11,13 and other ing species to internal redox changes of the dopants is phenomena. accounted for. Measurements on single crystals and on bicrystals with and without crack formation provide worthwhile information on the influence of free relaxed surfaces, II. Experimental Procedure freshly produced (crack) surfaces, and grain boundaries onMeasurements were performed on single crystals and bicrysthe surface reaction rate and diffusional process.

Recently it has been shown that the nearly free electron model for describing the electrical, magnetic and optical properties of expanded liquid caesium has already broken down by the time three times the critical density is reached, i.e long before the transition from the metallic to the non-metallic state occurs, which seems to coincide with the critical point of the liquid-vapour phase transition (Tc=1924 K, pc=92 bar, rho c=0.38 g cm-3). The authors discuss the deviations from the nearly free electron model within the framework of a consistent quantum statistical approach to the electrical conductivity, which leads to a generalized Ziman formula, taking into account electron-electron scattering, arbitrary degeneracy and screening. Further possible mechanisms that might contribute to the behaviour of the electrical conductivity, such as the formation of bound states are also discussed.

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