American Scientist

In this roundup, Fenella Saunders summarizes notable recent items about scientific research, selected from news reports compiled in the free electronic newsletter Sigma Xi SmartBrief.

Riding Raindrops

A raindrop can weigh 50 times more and travel 10 times faster than a mosquito, but the insects can still fly through a downpour without damage. Researchers used high-speed video of captive mosquitoes subjected to a water jet to confirm this finding. A mosquito’s low mass and strong exoskeleton cause the drops to lose little momentum when they collide in midair, so the bugs receive small impact forces. The researchers also found that the insects go with the water flow, sticking to the front of the drop for up to 20 body lengths, but their long legs and wings provided enough drag for them to rotate free before hitting the ground. (Image courtesy of David Hu.)

Dickerson, A. K., et al. Mosquitoes survive raindrop collisions by virtue of their low mass. Proceedings of the National Academy of Sciences of the U.S.A. 109:9822–9827 (June 19)

Cooler Hydrogen

Hydrogen is considered an alternative energy source, but one major means of obtaining it—splitting water atoms—requires a lot of electricity, which is often generated by fossil fuels. Researchers have developed a way to split water using heat and catalysts, but at relatively low temperatures and without corrosive intermediate products. They use manganese oxide and shuttle sodium ions in and out of it while heating, which drives off oxygen that bonds with the oxygen in added water. With the sodium, temperatures could be kept to around 850 degrees Celsius instead of over 1,000 degrees. The researchers found that the materials could be reused at least five times, but more surface area and higher proven reusability rates would be needed to scale up this process to an industrial level. They also hope to get the required temperatures down to the point where waste heat from steel mills or power plants could be used to run the process.

Xu, B., et al. Low-temperature, manganese oxide-based, thermochemical water splitting cycle. Proceedings of the National Academy of Sciences of the U.S.A. 109:9260–9264 (June 12)

Artificial Rat-Jellyfish

Using a flower-shaped piece of silicone and muscle cells from a rat heart, researchers have built a synthetic jellyfish. When placed in an electric field, the petals convulse downward and the device pulsates forward, swimming much like its natural namesake. Researchers mapped the cells of juvenile moon jellies (Aurelia aurita) and found that electrical signals spread through the animals’ muscles in a smooth wave as they swam. They grew a single layer of rat heart muscle on a patterned polymer membrane to mimic the contraction pattern. The investigators built the device to better understand the fundamental workings of muscular pumps, and think it could be a platform to test medications that aim to improve heart-pumping activity. (Image courtesy of Harvard University and Caltech.)

Nawroth, J. C., et al. A tissue-engineered jellyfish with biomimetic propulsion. Nature Biotechnology (published online July 22)

Do Not Pass

Planets outside of our solar system (dubbed exoplanets) are usually studied when they transit, passing in front of or behind their parent stars. One of the first exoplanets discovered, called Tau Boötis b, does not transit as viewed from Earth. Now high-resolution spectroscopy from a telescope in Chile has captured light from the exoplanet for the first time, and measurements of the planet’s carbon monoxide absorption have been made. From these readings, astronomers have calculated that the planet is orbiting at an inclination of about 44 degrees and has a mass about six times that of Jupiter. The technique could be used to detect atmospheres on other exoplanets that do not transit. (Image courtesy of ESO/L. Calçada.)

Brogi, M., et al. The signature of orbital motion from the dayside of the planet Tau Boötis b. Nature 486:502–504 (June 28)

Toothsome Diets

A trip to the dentist usually involves getting rid of plaque from teeth, but such buildup on ancient human fossils has been a boon to researchers studying early hominin diets. Analysis of the tartar on teeth of a 2-million-year-old hominin called Australopithecus sediba shows that they ate leaves, fruits and bark, suggesting they lived in a woodland environment. Dental wear and carbon ratios in the tooth chemistry supported the findings. Previously described diets of other early hominins pointed to an open savannah habitat. This was the first time that tartar has been found in such an ancient hominin. It is possible that the individuals lived during a time of drought and were forced to eat such foods because of lack of other resources. (Image courtesy of Amanda Henry.)

Henry, A. G., et al. The diet of Australopithecus sediba. Nature 487:90–93 (July 5)