We investigate the distribution of relative velocities between small heavy particles of different sizes in turbulence by analyzing a statistical model for bidisperse turbulent suspensions, containing particles with two different Stokes numbers. This number, St, is a measure of particle inertia which in turn depends on particle size. When the Stokes numbers are similar, the distribution exhibits power-law tails, just as in the case of equal St. The power-law exponent is a nonanalytic function of the mean Stokes number St[over ¯], so that the exponent cannot be calculated in perturbation theory around the advective limit. When the Stokes-number difference is larger, the power law disappears, but the tails of the distribution still dominate the relative-velocity moments, if St[over ¯] is large enough.

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A new approach for the encapsulation of laccases with enhanced activity and stability by biomimetic silica mineralisation is reported. A range of lignin model compounds, which includes syringol, syringyl acid, 4-vinylphenol, gallic acid, vanillic acid and guaiacol, was oxidised to lignin-type polymers by the silica-immobilised laccase systems at room temperature. The oxidation rate of the immobilised systems was lower than that of the free enzyme counterparts, but interesting products were observed with the new bio-catalytic materials, which showed reusability and good stability.

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