Ancient worms in armour

Abstract

negligible, effect. Now, engineering phonon drag would seem poised to become a new tool for improving thermoelectric materials. Although size seems to be the decisive difference between the two sets of results 3,4 , there are other possibly crucial differences between them: surface roughness, nanowire length and substrate material (in Boukai and colleagues' study 3 , the nanowire array was suspended above a silicon wafer; in Hochbaum and col-leagues' study 4 , it was bedded on silicon dioxide). Sorting out all the science behind these results might take time. We need to develop predictive models, understand the optimum size and doping levels, extend the data to high temperatures, and find out what other materials might show the effects of low thermal conductivity and large phonon drag. And does one really need nanowires at all, or would some other nanoscale configuration do? In one stroke (albeit from two directions), the thermoelectric capability of silicon has been improved by a factor of nearly 100. It thus leaps up the scale of thermoelectric materials from 'terrible' to 'not bad'. What happens next is any-one's guess; but I for one am no longer taking bets against silicon's thermoelectric future. ■ Cronin B. Vining is at ZT Services, It requires a quirk of fossilization for the soft parts of an animal to be preserved. Study of such a specimen of the mysterious machaeridians provides these organisms with a well defined evolutionary home. Figure 1 | The machaeridians. Top, a complete machaeridian scleritome from 425-million-year-old deposits in New York state 3. Length, 5.4 mm. Bottom, dorsal reconstructions of presumed complete scleritomes (not to scale) showing the diversity of scleritomes within the three families of machaeridians 9-running upper to lower, the Lepidocoleidae, Turrilepadidae and Plumulitidae. The fossil specimen (top) is a lepidocoleid; that described by Vinther et al.