Scale Model for Armor
A living fossil could inspire tomorrow’s armor. Engineers at the Massachusetts Institute of Technology, funded by the U.S. Army, investigated the primitive fish Polypterus senegalus, nicknamed the “dinosaur eel” for the suit of armor it sports. In experiments mimicking bites from a predator, the researchers found that each scale is made of three layers on a bone support that all complement one another to defy penetration. The outer coat is the hardest and most resistant to sharp teeth. The middle is softer and dissipates energy by deforming. The last layer has a plywoodlike structure, which prevents cracks from spreading. The precise sequence of these layers critically preserves armor strength—for instance, replacing the outer and middle layers in simulations increased risk of the scale coming apart. These findings, posted online July 27 by Nature Materials, could illuminate how fish evolved and lead to more effective ways of designing armor.
Making a Stand
Three years ago northern and central African nations that form the Community of Sahel-Saharan States agreed to a continent-wide belt of trees to combat the remorseless spread of the Sahara Desert. This past June they laid the groundwork for the Great Green Wall of Africa by formally adopting a two-year, $3-million initial phase for the project.
Green barriers against the Sahara have been around since the 1960s, but most have been small in scale. In contrast, the Great Green Wall will be 15 kilometers wide and will involve stretches of trees from Mauritania in the west to Djibouti in the east—a distance of some 7,000 kilometers. The aim is to protect the Sahel Belt—the dry savanna south of the Sahara—and prevent its precious arable land from desertification. The trees would also provide a source of firewood, crops and jobs. Projects to water these trees—say, by harvesting rain—could also help communities irrigate their fields all year long or even help them raise fish.
Pilot planting efforts, using local trees such as acacia (below), were scheduled to have begun in September. Funding for the entire project—perhaps its main stumbling block—still remains tentative.
Philanthropists Bill Gates and Michael Bloomberg, New York City’s mayor, announced in July a $500-million commitment to fight global tobacco use, especially in developing nations, where the burden of addiction is more costly. The money will support tobacco-control efforts, such as increasing cigarette taxes, modifying tobacco’s advertising image and helping people quit.
No Ruling Out Life
The Mars Phoenix lander discovered evidence of perchlorate (ClO4) and water ice in Martian soil, NASA researchers announced in August. Perchlorate, a highly reactive chemical that can occur naturally in arid areas such as Chile’s Atacama Desert, was detected in two soil samples analyzed by Phoenix’s wet-chemistry laboratory. Considered harmful to fetuses, perchlorate provides fuel for some microbes. For that reason, the discovery says little by itself about the possibility of life on Mars, NASA scientists say. Water ice was also identified in chunks of soil vaporized by Phoenix’s gas-analyzing instrument. The result confirms 2002 observations by the Mars Odyssey orbiter, which detected ice in the form of subsurface hydrogen atoms at the planet’s poles. In light of these successes, the space agency extended the Phoenix mission by five weeks, to September 30.
Keeping tabs on the HIV/AIDS epidemic is crucial for formulating treatment and prevention strategies, but the U.S. has greatly underestimated the annual number of new infections. An assay that differentiates between recent and long-standing infections has led scientists to conclude that 56,300 individuals in the U.S. contracted the virus in 2006; previous annual estimates had it at 40,000. African-Americans (83.7 infections per 100,000) and Hispanics (29.3 per 100,000) continue to be disproportionately affected compared with whites (11.5 per 100,000). The results, in the August 6 Journal of the American Medical Association, follow disappointing news about HIV vaccines, including the cancellation of a large trial called PAVE 100.