American Scientist

This roundup summarizes some notable recent items about scientific research, selected from news reports compiled in Sigma Xi’s free electronic newsletters.

Aurora Triggers

The dancing colors of the Northern Lights are actually electrical storms, created by magnetic fields and charged particles from the Sun. But what sets off these events? The NASA Themis mission, made up of five satellites designed to observe geomagnetic activity, may have found the answer. The Earth's magnetosphere stores the energy from the solar wind, then releases it suddenly. The trigger happens when the field lines from the solar wind and the magnetosphere are oppositely polarized, causing them to disconnect on the Sunward side of the planet and snapping them back together on the far side of the Earth. If this reconnection isn't fast enough, energy builds up in the tail region of the magnetosphere and is rapidly emitted when the field lines converge. Better predictions of the advent of these colorful geomagnetic storms may help to prevent disruption of satellites in orbit and power grids on the ground.

Angelopoulos, V., et al. Tail reconnection triggering substorm onset. Science 321:931–935 (August 15)

Wind Turbines Give Bats the Bends

For reasons unknown, bats seem to be attracted to large wind turbines. The potential for accidents is obvious, but bats are killed about half the time not from impact, but from hemorrhaging. Near the turbine blades, the drop in air pressure causes fatal damage to the bats' lungs, much like a case of the bends in divers or air passengers who ascend too quickly. Turbine blades create lift, like an airplane wing, which suddenly and dramatically drops pressure in a small zone around the tips of the blades. This change expands the lungs of bats flying through these zones, causing fine capillaries to burst and the lungs to fill with fluid, essentially drowning the animals in mid-air. Migrating bats experienced most of the fatalities, so it may be possible to minimize the damage by changing turbine schedules during peak migration periods.

Baerwald, E. F., et al. Barotrauma is a significant cause of bat fatalities at wind turbines. Current Biology 18:R695–R696 (August 26)

Springy Robot Legs

For a robot, walking is an incredibly complicated task. Human muscles and tendons recapture up to 40 percent of the energy of the step to create an efficient gait. Oregon State University roboticists have now created a robot leg that uses steel cable "tendons" and built-in fiberglass springs, made of the same material as an archer's bow, to store and release energy. Each spring stores sufficient power for a single hopping step; to get the same power from a motor alone would require 30 times the weight. The legs walk well on even ground, but the researchers are now working on getting them to run and to traverse rough terrain.

Hurst, J. W., and A. A. Rizzi. Series compliance for an efficient running gait. IEEE Robotics and Automation Magazine, 15:42–51 (September)

Wandering Stars

Stars in spiral galaxies, it was thought, remain at roughly the same distance from their galaxy's center as when they originally formed. New computer simulations show that this might not be the case. The simulations start with conditions that were in place about 9 billion years ago for a galaxy much like ours, then allow the galaxy to evolve on its own. If a star during its orbit around the center of the galaxy intercepts a spiral arm of the galaxy, its orbit still remains stable and circular, contrary to previous theories. However, the size of its orbit can become much larger or smaller, changing its distance from the galaxy center significantly. Such developments could alter theories of what creates habitable zones in galaxies.

Roskar, R., et al. Riding the spiral waves: implications of stellar migration for the properties of galactic disks. The Astrophysical Journal Letters 684:L79–L82 (September 10)

Obesity Is a Headache

In addition to the numerous other health problems related to childhood obesity, overweight kids have now been found to have more headaches. A connection between headaches and obesity had already been established in adults. The study of more than 900 youngsters at seven U.S. headache centers over a period of six months found that the more overweight children were, the more headaches and the worse the pain they experienced. Obese children who lost weight during the study reported about half as many headaches as those who continued to gain weight. There was no correlation between headaches and weight gain or loss for children of normal weight. Causes for the headaches could include dehydration and stress, but obese adults with migraines have been found to have low levels of a hormone that causes a feeling of fullness after eating.

Hershey, A. D., et al. Obesity in the pediatric headache population: a multicenter study. Headache (published online September 9)

Eyes on Autism

People with autism tend to be socially withdrawn, lacking communication skills and finding it hard to infer what others are thinking or feeling. Williams syndrome, by contrast, makes people hypersocial, with exceptional language and interaction skills, but often unable to inhibit social responses. A new study shows that differences in social scene perceptions may characterize these opposite disorders. Individuals were observed with an eye-tracking device while they looked at photographs of scenes containing people. Those with Williams syndrome spent more time looking at faces, particularly eyes, than is typical, indicating that they may be unable to inhibit themselves from staring. People with autism tended to focus on parts of the scene that are not socially relevant, such as chairs or people's bodies, and spent far less time on faces and eyes. In both cases there may be evidence that a relationship between the prefrontal cortex, which inhibits behavior, and the amygdala, which is involved in emotion processing, could be crucial in the development of these disorders.

Riby, D. M., and P. J. B. Hancock. Viewing it differently: social scene perception in Williams syndrome and autism. Neuropsychologica 46:2855–2860 (September)