Developments to Watch
A MEETING OF MINDS IN PHILADELPHIA
Science takes on diodes, disease, dopamine, and the defense of Dolly
The 150th gathering of the American Association for the Advancement of Science had a distinguished guest list: President Bill Clinton opened the event in Philadelphia last week with a call for strong antitobacco legislation. Also in attendance were Ian Wilmut, who cloned the famed sheep Dolly; U.S. Surgeon General Dr. David Satcher; and U.S. Supreme Court Justice Stephen G. Breyer, who discussed science in the courts. Here are some of the highlights.Return to top
LASER DIODES MAKE A QUANTUM LEAP
FEDERICO CAPASSO, A SOLID-STATE physicist at Bell Laboratories, says he has created a new type of laser on a chip--a laser diode--that is both practical and 100 times as powerful as existing devices. Today's laser diodes, widely used in bar-code readers and CD-ROM drives, give off photons of light when electrons and positively charged "holes" recombine on the chip. Capasso's diode uses a different mechanism--a quantum-mechanics effect known as resonant tunneling, in which units of charge cascade down a series of quantum "waterfalls," giving off photons with each jump.
For the new diodes, that means a single electron can give off some 25 photons, instead of just one, says Capasso. And there's another big advantage: The color, or wavelength, of light can be tuned for different purposes by altering the thickness of the chip's layers. Conventional laser diodes, in contrast, require different materials for each color.
Capasso and his team first demonstrated their cascade devices in 1994. But those worked only when cooled to very low temperatures. The new device performs at room temperature, which makes it commercially viable. "There is nothing comparable out there," Capasso says. He predicts that the lasers will first be used as long-range sensors--to measure air pollutants from as far as two kilometers away.By John CareyReturn to top
WHY CHOCOHOLISM WILL NEVER DIE
THE LATIN NAME FOR THE cacao tree, Theobroma, means "food of the gods," and who wouldn't agree? Now, researchers have discovered that no other food can satisfy the craving for chocolate, even if the substitute contains many of the same chemicals.
A recent University of Pennsylvania survey found that one-third of adults say they regularly crave chocolate--which could be why yearly U.S. consumption is 12 pounds per person. Scientists had assumed that the craving was linked to one or more of the 300 chemicals contained in chocolate, such as substances similar to caffeine and dopamine.
Not so, says Paul Rozin, a Penn psychologist. He asked 30 volunteers to record the effect of various substances on their yen for chocolate. Coffee didn't dull it, nor did capsules of cocoa powder. Other combinations of cocoa, sugars, and fats fared only slightly better. The only food that reduced the craving was an actual chocolate bar. "There's just something about having this wonderful substance in your mouth," says Rozin. Warning: Testing this theory could cause weight gain.By Catherine ArnstReturn to top
HEALTHY GENES FOR UNHEALTHY LUNGS
GENE THERAPY HAS BEEN long on promise but short on results. The basic problem is delivering the genes. For example, to treat cystic fibrosis, scientists have inserted correct copies of the gene that causes the illness, using a virus as the delivery "vehicle." But in clinical trials, the new gene never worked for long. And repeated treatments tended to make things worse, provoking immune responses against the virus.
Scientists at Genzyme Corp. say that in recent tests they got better results using molecules called lipids as a delivery vehicle. When the molecules, which get gobbled up by target cells, were hitched to correct versions of the CF gene and inserted into patients' lungs, the benefits lasted up to several weeks. The results provide hope that an improved lipid, already being developed at Genzyme, could provide an effective treatment, says Genzyme senior director Seng H. Cheng.By John CareyReturn to top