Blocking Sound with Holes
Anyone kept awake by a neighbor’s television may be surprised to learn that a few holes drilled through a wall could lower the volume on sound. Francisco Meseguer of the Polytechnic University of Valencia in Spain and his colleagues placed a series of 20-centimeter-thick aluminum plates in a tank of water and found that perforated plates could diminish ultrasound waves passing through by up to another 10 decibels as compared with solid plates. This reduction was greatest when the spacing between the holes roughly equaled the sound’s wavelength. Evidently, the incoming sound interacts with regularly spaced holes, generating acoustic waves on the plate’s surface that destructively interfere with waves going through the plate. The findings, in the August 22 Physical Review Letters, could help soundproof machines while allowing cooling air through, remarks Meseguer, who says his team is now experimenting with audible sound.
—Charles Q. Choi
More Fluid Mileage
Electric fields can boost a car’s gas mileage by up to 20 percent, thanks to a well-known effect in which electric fields reduce the viscosity of a liquid [see “Electrorheological Fluids”; Scientific American, October 1993]. Reduced fuel viscosity means that much smaller droplets can be injected into the engine, leading to more efficient combustion. Investigators at Temple University thinned fuel by attaching an electrically charged tube to a diesel engine’s fuel line near the fuel injector. In road tests, the attachment, which consumed less than 0.1 watt, increased highway fuel economy from 32 to 38 miles per gallon. The researchers, who describe the boost in the November 19 Energy & Fuels, expect the device will find use in all kinds of internal-combustion engines.
—Charles Q. Choi
Every night the Brazilian ant Forelius pusillus takes selflessness to a whole new level. At dusk, as the ants defend their homes by sealing off the entrances with sand, up to eight workers remain outside to finish the job. Left behind, they die by the next day—the first known example of a suicidal mission that is preemptive rather than a response to immediate danger.
Behavioral ecologist Adam Tofilski of the Agricultural University of Kraków in Poland and his colleagues found that these ants were not just stragglers trapped outside. They were deliberately helping to cover the entrances, spending up to 50 minutes kicking sand into the holes until the entrances were indistinguishable from the surroundings. In experiments, the scientists found that only six of 23 ants left behind were alive the next morning, showing that their act was a sacrifice. Just why the ants died is unclear—the species is fragile, but the researchers also suspect that the outside individuals could be old or sick. The findings, in the November American Naturalist, could elucidate the evolution of altruism.
—Charles Q. Choi
The 2008 Nobel Prizes
This month the king of Sweden will honor these 10 people of science for their achievements.
Three of them—Luc Montagnier, Yoichiro Nambu and Paul Krugman—have written for Scientific American.
Physiology or Medicine: Harald zur Hausen of the German Cancer Research Center in Heidelberg, for his discovery that the human papillomavirus causes cervical cancer, and Françoise Barré-Sinoussi of the Pasteur Institute in Paris and Luc Montagnier of the World Foundation for AIDS Research and Prevention in Paris, for their discovery of the human immunodeficiency virus (HIV). In making its choice, the Nobel committee snubbed Robert C. Gallo of the University of Maryland, who proved that HIV causes AIDS.
Physics: Yoichiro Nambu of the University of Chicago, for the discovery of the mechanism of spontaneous broken symmetry, which helps to explain the masses of subatomic particles and the forces acting on them, and Makoto Kobayashi of the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan, and Toshihide Maskawa of Kyoto University, for the discovery of the origin of broken symmetry, which predicts the existence of at least three families of quarks.