Ray Baughman creates artificial muscles
Nature has been developing her technologies for many hundreds of millions of years, said Ray Baughman. “By looking at the way in which nature has solved problems like muscles, we can advance our own technologies.” Baughman is director of the NanoTech Institute at the University of Texas at Dallas. His lab creates very tiny artificial muscles by spinning filaments of invisibly small carbon nanotubes into an extraordinary yarn. Pound for pound, this nano-yarn is stronger than steel – yet is so light it almost floats in air.
Are zebra stripes just an elaborate insect repellent?
“How the zebra got his stripes” sounds like the title of one of Rudyard Kipling’s “Just So” stories. Sadly, it isn’t, so the question has, instead, been left to zoologists. But they, too, have let their imaginations rip. Some have suggested camouflage. (Charles Darwin pooh-poohed that idea, pointing out that zebra graze in the open, not amid thick vegetation where a striped pattern might break up their outlines.) Others suggest they are a way to display an individual’s fitness. Irregular stripes would let potential mates know that someone was not up to snuff. One researcher proposed that stripes are to zebra what faces are to people, allowing them to recognise each other, since every animal has a unique stripe-print. Another even speculated that predators might get dizzy watching a herd of stripes gallop by.
There is, however, one other idea: that stripes are a sophisticated form of fly repellent. It was originally dreamed up in the 1980s, but never proved. Now, a team of investigators led by Gabor Horvath of Eotvos University in Budapest report in the Journal of Experimental Biology that they think they have done so.
The original suggestion was that stripes repel tsetse flies. These insects carry sleeping sickness, which is as much a bane of ungulates as it is of people. But tsetses are not the only dipteran foes of zebra and, since they are rarely found in the meadows of Hungary, Dr Horvath plumped for studying an almost equally obnoxious alternative: the horsefly.
Horseflies, too, transmit disease. They also bite incessantly, thus keeping grazing beasts from their dinner. Indeed, previous research has shown that fly attacks on horses and cattle reduce their body fat and milk production. Such research has also shown something odd: horseflies attack black horses in preference to white ones. That fact got Dr Horvath wondering how they would react to a striped horse—in other words, a zebra.
Actual zebra are hard to experiment on. They insist on moving around and swishing their tails. The team therefore conducted their study using inanimate objects. Some were painted uniformly dark or uniformly light, and some had stripes of various widths. Some were plastic trays filled with salad oil (to trap any insect that landed). Some were glue-covered boards. And some were actual models of zebra. They put these objects in a field infested with horseflies and counted the number of insects they trapped.
Their first discovery was that stripes attracted fewer flies than solid, uniform colours. As intriguingly, though, they also found that the least attractive pattern of stripes was precisely those of the sort of width found on zebra hides. Zebra stripes do, therefore, seem to repel horseflies.
Exactly why is unclear. But Dr Horvath thinks it might be related to a horsefly’s ability to see polarised light, which imposes a sense of horizontal and vertical on an image. Horseflies are known to prefer horizontal polarised light. Possibly, the mostly vertical stripes on a zebra confuse the fly’s tiny brain and thus stop it seeing the animal.
Another obvious question, though, is why other species have not evolved this elegant form of fly repellent, and what the consequences would have been if they had. If humans, for example, were black-and-white striped then the history of intercommunal violence the species has suffered when different races have met might not have been quite as bad. One for Kipling to have pondered, perhaps?
Source: The Economist
Not a scratch
Scorpions may have lessons to teach aircraft designers
The north African desert scorpion, Androctonus australis, is a hardy creature. Most animals that live in deserts dig burrows to protect themselves from the sand-laden wind. Not Androctonus. It usually toughs things out at the surface. Yet when the sand whips by at speeds that would strip paint away from steel, the scorpion is able to scurry off without apparent damage. Han Zhiwu of Jilin University, in China, and his colleagues wondered why.
Their curiosity is not just academic. Aircraft engines and helicopter rotor-blades are constantly abraded by atmospheric dust, and a way of slowing down this abrasion would be welcome. Dr Han suspects that scorpions may provide an answer. As he writes in Langmuir, he has discovered that the surface of Androctonus’s exoskeleton is odd. And when that oddness is translated into other materials it seems to protect them, as well.
Dr Han’s investigations began by scouring the pet shops of Changchun, where the university is located, for scorpions. Having obtained his specimens, he photographed them under a microscope, using ultraviolet light. This made the animals’ exoskeletons, which are composed of a sugar-based polymer called chitin, fluoresce—thus revealing details of their surface features. The team found that Androctonus armour is covered with dome-shaped granules that are 10 microns high and between 25 and 80 microns across. These, they suspected, were the key to its insouciance in the face of sandstorms.
To check, they took further photographs. In particular, they used a laser scanning system to make a three-dimensional map of the armour and then plugged the result into a computer program that blasted the virtual armour with virtual sand grains at various angles of attack. This process revealed that the granules were disturbing the air flow near the skeleton’s surface in ways that appeared to be reducing the erosion rate. Their model suggested that if scorpion exoskeletons were smooth, they would experience almost twice the erosion rate that they actually do.
Having tried things out in a computer, the team then tried them for real. They placed samples of steel in a wind tunnel and fired grains of sand at them using compressed air. One piece of steel was smooth, but the others had grooves of different heights, widths and separations, inspired by scorpion exoskeleton, etched onto their surfaces. Each sample was exposed to the lab-generated sandstorm for five minutes and then weighed to find out how badly it had been eroded.
The upshot was that the pattern most resembling scorpion armour—with grooves that were 2mm apart, 5mm wide and 4mm high—proved best able to withstand the assault. Though not as good as the computer model suggested real scorpion geometry is, such grooving nevertheless cut erosion by a fifth, compared with a smooth steel surface. The lesson for aircraft makers, Dr Han suggests, is that a little surface irregularity might help to prolong the active lives of planes and helicopters, as well as those of scorpions.
Source: The Economist