The new micro-fans could aid the development of faster, smaller laptop computers and allow portable electronics manufacturers to pack more chips – and therefore more fancy features – into their products.

Keeping chips cool is important because heat decreases their performance and reliability. But to satisfy consumer demand for smaller gadgets that do more stuff, manufacturers have had to cram more circuitry into smaller spaces – which only adds to the heat problem.

The new fans consist of polyester or metal blades (about 2 cm by 0.5 cm) attached to tiny patches of “piezoelectric” ceramic. An alternating current applied to the ceramic causes it to expand and contract, making the blades wave back and forth like an old-fashioned Chinese folding fan.

In principle, the design could be an improvement over the rotational fans commonly used in laptops, says Mark Spearing at the Massachusetts Institute of Technology. It is possible to make very small rotational fans – a team at the University of Colorado at Boulder have one that fits on the head of a pin. But Spearing says that at smaller sizes, frictional forces make them less efficient.

Heat budget

Efficiency is critical because the energy used to move the fan blades eventually gets dissipated as heat – meaning an inefficient fan could add heat, not lose it.

However Spearing remains unconvinced that piezoelectric fans are the answer. “I suspect that the air flow rates that can be achieved are very low, and will therefore not be effective for chip cooling.”

Garimella concedes the piezoelectric fans probably cannot move as much air as a rotational fan, but he says they are designed to work with rotational fans in laptops, not replace them.

When Garimella put a piezoelectric fan inside a laptop computer with a rotational fan, it brought the temperature down by 8°C. The piezoelectric fans are far less power hungry, he says, using about one per cent of the power needed by rotational fans.

Cool and quiet

Piezoelectric fans could be also be used to break up pockets of hot air in tiny spaces that rotational fans cannot reach. Garimella eventually hopes to build fans with 100 micrometre blades that could be attached directly to computer chips.

Finally, piezoelectric fans do not make any noise – a feature that makes them especially well-suited for use in cell phones.

The team will present their findings at the Thermal Challenges in Next Generation Electronic Systems conference in Santa Fe, New Mexico, in January 2002.

Vincent Fischetti and colleagues at Rockefeller University in New York isolated the enzyme, called Pal, from a bacteriophage (a type of virus that infects bacteria) that targets S. pneumoniae.

Earlier this year, Fischetti’s team isolated another bacteriophage enzyme that kills streptococci, the bacteria responsible for strep throat. The same method could also be used to find enzymes that kill other bacteria. “Every bacteria has a bacteriophage system,” Fischetti says.

S. pneumoniae lurks in the nose and throat of half the human population and is a significant source of illness and death worldwide. It can cause problems ranging from ear infections to potentially deadly diseases like pneumonia and meningitis.

“Exciting opportunity”

In test tube experiments, Pal killed 15 strains of S. pneumoniae within seconds of contact, but did not interfere with other, harmless, bacteria that grow in the nose and throat, or with human cells. The enzyme also proved effective against S. pneumoniae when applied to the noses of infected mice.

Fischetti is now planning clinical trials to test a nasal spray containing Pal. He says the spray could be used periodically, say once a week, to keep bacteria under control.

“I think it’s an exciting opportunity for both prevention and treatment,” says Cynthia Whitney, an epidemiologist at the Centers for Disease Control in Atlanta. She says the spray might be especially useful in day care centres and nursing homes, where infections can spread quickly from person to person.

Fischetti says Pal would be more effective than existing vaccines, which only protect against individual strains of S. pneumoniae. And because the enzyme is so deadly, the bacteria do not seem to be able to acquire resistance, as they have to antibiotic drugs, he says.

Journal reference: Science (vol 294, p 2170)

The team, led by John Terborgh of Duke University, conducted a census of the herbivores and trees on several islands in Lago Guri, a 4300 square kilometre lake in Venezuela that was created in 1986 when a river was dammed for hydroelectric power.

When the water rose, the smallest of the islands lost nearly all of the predatory animals that inhabit the mainland, such as jaguars, snakes and raptors. The situation provided a unique natural experiment to test two competing theories of how ecosystems are structured.

The so-called bottom-up theory, says, in effect, that the plants are in control. Proponents of this idea argue that the availability of edible plants determines how many herbivores an ecosystem can support, which in turn determines how many predators it can support.

The top-down theory, on the other hand, argues that the predators are in charge. They keep the herbivores in check, thereby determining the abundance of plants.

Population explosion

“Some theoretical ecologists have argued that these top-down effects aren’t very important or very common,” says Michael Pace of the Institute of Ecosystem Studies in Millbrook, New York. “But these kinds of observations are very hard to make in terrestrial ecosystems, which is why it’s been so hard to tell.”

Until now. The bottom-up theory predicts nothing much should have changed in the Lago Guri after the predators disappeared. But Terborgh’s findings show that the absence of predators has had a profound effect on the islands’ ecosystems.

His team found that herbivores such as howler monkeys, iguanas and leaf-cutter ants were 10 to 100 times more prevalent on the lake’s six smallest islands than they were on the mainland. The density of young trees on these islands was less than half that on six larger islands in the lakes, which had retained some of their predators.

Back lash

Pace says the study illustrates nicely that top-down processes can shape ecosystems, at least in some situations. However, he adds that the pendulum could swing back to bottom-up forces if the herbivores gobble up all the edible plants on the islands. If that happens, the remaining plants could begin limiting animal populations.

The study’s authors argue that predators play a key role in maintaining biodiversity. An overabundance of herbivores “threatens to reduce species-rich forests to an odd collection of herbivore-resistant plants,” they write. “Along the way, much plant and animal diversity will probably be lost.”

This process is already happening in North America, they say, where deer populations have ballooned, and in Malaysia, where wild pigs run rampant through some forests.

Journal reference: Science (vol 294, p 1923)

A Swedish ecologist is proposing the idea as an environmentally friendly alternative to burial and cremation. “If you come from the soil, you should also give back to it,” says Susanne Wiigh-Masak, an environmental consultant based in Lyrö, Sweden. Her proposals have already won provisional approval from the Church of Sweden.

Wiigh-Masak says there are problems with both cremation and burial. She estimates that crematoria use the equivalent of 50 litres of oil to reduce a body to ash. They also release toxic chemicals into the atmosphere, such as mercury vapour from dental fillings and cancer-causing polyaromatic hydrocarbons.

Green grave

Burial is also not as green as it might seem. In many countries, bodies have to be embalmed. A corpse buried in a coffin then takes 50 to 60 years to decompose, and as it does so, embalming chemicals such as formaldehyde can pollute the groundwater. Wiigh-Masak says her method safely returns all organic compounds to the soil within six months.

Wiigh-Masak has tested her technique on dead pigs and cows. She immerses the carcasses in a bath of liquid nitrogen at less than ­196 °C, while bombarding them with ultrasound waves to crack open the tissue so the nitrogen can penetrate and deep-freeze the carcasses right to the core. Applying a vacuum removes water from the remains.

“What you are left with is a hygienic, odourless powder that is less than one per cent water,” Wiigh-Masak says. An 80 kilogram body produces about 20 kilograms of powder, which can be placed in a biodegradable coffin and buried in a shallow grave.

Life after death

Wiigh-Masak says she has had a number of inquiries from funeral homes. Many run crematoria that will soon have to be updated to meet Swedish emissions laws, she says, and adopting her technology would be cheaper than upgrading them. She estimates the cost of freeze-drying bodies will be comparable to that of cremation.

Swedish law states that bodies must be embalmed and buried metres underground. But Wiigh-Masak says it is likely that the law will be relaxed to allow freeze-drying. In a recent newspaper poll in Sweden, 40 per cent of those questioned said they approved of the method, while very few actively opposed it. The Church of Sweden also gave her its blessing. “My method is very close to their reading of the Bible,” she says.

The Church of England would probably accept the procedure too, so long as it’s done in a dignified manner, says Geoffrey Rowell, the Bishop of Basingstoke and chair of a multi-faith committee on funerals. “The concern of the Church is that bodies are reverently disposed of,” he says.