In the News
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. Science in the News Daily is e-mailed
to subscribers each weekday; Science in the News Weekly,
which reviews the previous week and weekend in
science-related news, is produced in collaboration with
American Scientist Online. To sample the e-newsletters and sign
up, visit www.sigmaxi.org/sitn and www.americanscientist.org/sitnweekly.
Researchers Weave Nanotubes into Super-Strong, Lightweight
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
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
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
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
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).