SCIENCE

Researcher Anthony James said his team's work represents "the first time we have brought all the pieces together to create a stable model that can also reproduce."

In the study, the researchers took advantage of a vulnerability of the virus, which in its life cycle briefly has a double strand of RNA, rather than its usual single strand. At that point, the RNA can be cut by a naturally occurring protein called dicer-2, thereby destroying the genetic material. Once the process is started on the double-stranded RNA, the single-stranded RNA also becomes vulnerable, and the virus's ability to replicate is destroyed.

The treated virus, which was then cloned and injected into mosquito embryos, "inoculated" the mosquitoes with an essentially benign form of the virus.

-- Marc Kaufman

The Shape of Weak Polymers

As every kid who's ever fashioned an overly ambitious Christmas cookie knows, there are some shapes that just don't travel well. Move them off the baking sheet and onto the cooling rack, and they're likely to break, often right in the middle.

It turns out that synthetic polymers -- complicated, man-made chemical compounds -- sometimes suffer the same fate. Sergei S. Sheiko, a chemist at the University of North Carolina at Chapel Hill, described the problem in last week's Science.

He and his colleagues made numerous compounds shaped like bottle brushes. Each had a backbone of carbon atoms linked in a chain. Coming off the backbone, like bristles, were side chains made of linked carbons. Compounds such as these are called polymers.

The researchers then transferred each polymer to a flat surface -- mica, graphite or silicon. Sometimes the surface was lubricated with a liquid made of water-and-alcohol mixtures. The surfaces exerted different pulls on the molecule as it spread out on the surface, trying to lie as flat as possible.

The researchers found that if the side chains were too long or too close to each other, the pull was too much and the backbone broke.

Polymers with the longest or most densely spaced side chains broke the most. Eventually, though, each would reach a stable size -- a shattered cookie reduced to pieces of durable, uniform size.

What was unusual about this finding is that carbon-carbon bonds are very strong. They are very hard to break (which is one reason that carbon compounds are the basis of living things). Yet in these experiments, the bonds were breaking under simple, old-fashioned mechanical stress.

As scientists cook up more compounds to do nano-scale work on all sorts of surfaces, this is a good thing to know.

-- David Brown