American Scientist

This roundup of notable recent items about scientific research, culled from news reports, was compiled from two free electronic newsletters produced by Sigma Xi's Public Understanding of Science program.

Researchers Weave Nanotubes into Super-Strong, Lightweight Sheets

Scientists have squeezed carbon nanotubes into ribbons 2,000 times flatter than a human hair and 5 centimeters wide. The sheets maintain the remarkable strength, flexibility and conductivity of their cylindrical precursors. Nanotubes have been the subject of near-fantastical promise and speculation since their discovery in 1991, but engineers had so far failed to weave the spongy carbon molecules into materials for larger applications. In this study, investigators created clumps of nanotubes inside of a drum and used sticky paper to coax out one row. They let Van der Waals forces hitch the next row onto the first, then repeated the process until the rows were assembled into loosely-packed sheets. Those sheets were then quickly spun down into dense ribbons.

Zhang, M., et al. Strong, transparent multifunctional, carbon nanotube sheets. Science 309:1215-1219 (August 19).

New Research Pegs TB at 3 Million Years Old

Tuberculosis has much deeper roots than originally thought. Scientists had believed that the disease, caused by Mycobacterium tuberculosis,took off just tens of thousands of years ago. But a rare strain of the bacterium that turned up a few years ago in Africa has altered that view. Analysis of its genetic data suggested that it descends from a species of bacterium estimated to be 3 million years old. The study says this bacterium caused a form of TB that afflicted hominids who migrated the disease around the world, making TB the oldest human affliction on record.

Gutierrez, M. C., et al. Ancient origin and gene mosaicism of the progenitor of Mycobacterium tuberculosis. Public Library of Science Pathogens 1:1:001-007 (September).

Earth's Core Spins Faster Than Its Surface

Some seismologists put forward the idea in 1996 that Earth's solid inner core spins a bit faster than the surface, but others challenged the findings. So the original team found better data: They isolated two earthquakes of almost identical location and size, separated only by years, and compared the seismic waves each produced. There was a difference in the waves' forms and in the time it took for them to travel all the way through the planet. This indicated that some geophysical shift had occurred in the inner core. Working from the time gap, the researchers figured the inner core was rotating from 0.3 to 0.5 degrees faster per year than the surface.

Zhang, J. et al. Inner core differential motion confirmed by earthquake waveform doublets. Science 309:1357-1360 (August 26).

Icy Collisions in Clouds Spark Lightning

Pictures taken by satellite radar show that clouds laced with lots of ice produce more lightning. The increased electrical output occurred whether the clouds were over the Himalaya Mountains, the Florida coast or the rain forests of northern Australia.

What's at work? Inside storm clouds, precipitation-sized particles of ice—a millimeter or more across—crash into smaller ice particles that are whipped around by swirling winds. Collisions cause a separation of electrical charge: Smaller ice pebbles are pushed up to the top of the cloud, carrying a positive charge; the heavier ice particles carry a negative charge and sink to the bottom of the cloud, turning each cloud into a big battery.

Petersen, W. A., et al.TRMM observations of the global relationship between ice water content and lightning. Geophysical Research Letters 32:L14819 (July 26).

Hurricanes Churn Up Immense Waves

Hurricanes frequently roil immense and mighty waves, according to new evidence. Last September oceanographers put sensors on the ocean floor in front of a furiously advancing Hurricane Ivan. The instruments sent back water-pressure readings, from which the height of the waves were deduced. In the Gulf of Mexico, Ivan produced 24 waves that were higher than 50 feet and one that reached more than 90 feet. These immense hurricane-generated waves did not reach land, however. Although a lot more common than tsunamis, these waves are whipped up by winds and so extend only from the water's surface. Tsunami waves are most often generated by seismic events that alter the sea floor, displacing huge volumes of water upwards.

Wang, D. W., et al. Extreme waves under Hurricane Ivan. Science 309:896 (August 5).

In Vertebrates, Stem Cells Work Together to Construct Neck

Biologists have pinned down the embryonic stem cells responsible for the structure of neck and shoulders in vertebrate animals. They have found a surprise: Two types of stem cells work together to build the neck, correctly matching up muscles to the appropriate bones. Physiologists had thought that groups of homogenous stem cells were set off in camps delineated by task—some growing the bones of the neck, while others were generating its muscle. They found instead that groups of stem cells actually make scaffolds first, coding the proper connections between muscle and bone. Other cells later actually fill in the bone and muscle.

Matsuoka, T., et al.Neural crest origins of the neck and shoulder. Nature 436:347-355 (July 21).