Clothes with a spark
It may not be too long before that new blazer or blouse recharges your BlackBerry.
A team of scientists at Georgia Tech has developed proof-of-concept fibers that generate small amounts of electricity when individual strands rub together – the way fibers might as a person walks. If the technology can be scaled up, the team envisions using it to power tiny sensors or surveillance devices for the military. Variations might also appear in clothing, curtains, or other fabric-based products.
For its experiments, the team formed fibers out of Kevlar, then grew tiny nanowires of zinc oxide on the fibers, giving them the look of a microscopic roller-style brush. They coated the nanowires on one strand with gold, to ensure that electric current would flow in only one direction, as it does in a battery. Then they rubbed the two strands back and forth against each other with an 80-r.p.m. motor. As the bristles brushed past each other, they bent back and forth, generating a small amount of electricity though a process called the piezoelectric effect.
For wash-n-wear, however, zinc oxide won't do. It doesn't get along well with water. The results appear in today's issue of the journal Nature.
Decoding Enceladus's plumbing
When the Cassini spacecraft first spotted an icy geyser on Saturn's moon Enceladus in 2005, the discovery raised a lot of eyebrows among planetary scientists. The geyser implied a sizable reservoir of liquid water beneath the surface, suggesting a subsurface habitat that could be suitable for simple life-forms. If that were true, Enceladus would join Jupiter's moon Europa as a target for future, biologically oriented space probes.
Now, scientists think they have figured out how Enceladus's system works, strengthening the case for a subsurface sea there. Based on Cassini's data, the scientists figure that only a large body of water can account for the constant stream of ice that erupts from the surface. The water temperature hovers around 32 degrees F. At that temperature, water can exist as a gas, liquid, and ice.
The team, led by Juergen Schmidt at the University of Potsdam, calculates that as the water vapor races up through cracks in the moon's crust (at up to 1,100 miles an hour) it expands. Droplets condense, turn to ice, and are borne upward by the remaining vapor. Because the crystals rattle off one another and off the sides of the fissures, they lose speed. So when they are ejected, most fall back to the moon's surface. The remaining vapor, by contrast, escapes the moon's gravity and keeps traveling until it's trapped in Saturn's magnetic field. It still carries a few of the smaller ice particles, which help build one of Saturn's rings – the E ring.
Other models of the moon's plumbing have been offered, but they don't account for the observed steady stream of material or the volume of material as this new model does. The results appeared in a recent issue of the journal Nature.
Farmed salmon may hurt wild ones
Salmon farming is taking a significant bite out of populations of wild salmon and its relatives on a global scale, according to a new study from scientists at Dalhousie University in Halifax, Nova Scotia. In many areas, wild salmon populations that encounter salmon farms shrink by more than 50 percent per generation, compared with far smaller losses for wild populations that don't encounter salmon farms.
Over the years, scientists have been trying to weigh the impact of fish farming on wild stocks, whose long-term decline in many areas trigger the move to farmed fish in the first place. Earlier studies have shown that parasites and diseases can be passed from farmed to wild salmon, and that the two interbreed.
Moreover, those conditions have been associated with declines in wild stocks. But this work gives the first global look at the question, the two scientists note. The duo looked at data covering Scotland and Ireland, as well as the Canadian Atlantic and Pacific regions.
The results suggest that to fully preserve wild stocks, regulators may need to move salmon farms to waters outside local salmon migration routes, require that the farms lie fallow during migration periods, or enforce tighter controls on parasites within fish farms. The results appear in the current issue of the online journal Public Library of Science-Biology.