SCIENCE
Notebook

Monday, October 23, 2006

'Invisible' to Microwaves

It isn't the kind of invisibility cloak that you could put on and then disappear, but scientists at Duke University say they have taken a step in that direction with a device that deflects microwaves.

Using "metamaterials" -- created from circuit board materials and metals -- the researchers fashioned rings about five inches in diameter. The structure was able to redirect any microwaves beamed onto it, creating a flow similar to river water streaming around a smooth rock. From a microwave perspective, the circular cloak and copper cylinder placed inside "disappeared."

"By incorporating complex material properties, our cloak allows a concealed volume, plus the cloak, to appear to have properties similar to free space when viewed externally," said David R. Smith, a professor of electrical and computer engineering at Duke. "The cloak reduces both an object's reflection and its shadow, either of which would enable its detection.''

The cloaking structure -- based on a new theory proposed by John Pendry of Imperial College London -- was described by team members as a "baby step" on the way to making things invisible as non-scientists would understand it.

Creating a device that would cloak wavelengths in the visible spectrum, making objects disappear to sight, would be vastly more difficult. Viewers can see things because objects redirect and scatter the light that strikes them, reflecting some of those wavelengths back to the eye. To make them disappear would require warping all the varied light wavelengths present.

The experiment was reported in Friday's issue of the journal Science just five months after the team first published its theory that such cloaking should be possible.

-- Marc Kaufman

Dinosaurs Survived One Meteor

Mounting evidence suggests that the long-standing chief suspect in the demise of the dinosaurs -- a meteor that slammed millions of years ago into the Yucatan peninsula near what is now Chicxulub, Mexico -- had an even deadlier accomplice. The new scenario holds that the Chicxulub meteor, combined with gigantic volcanic eruptions in what is now India and the worldwide climate change that followed, put the dinosaurs and many other species on the brink of extinction.

But it took another, as yet undiscovered, meteor impact 65.5 million years ago to finally bring the end of the Age of Reptiles, a paleontologist says.

Fossils obtained from sediments drilled from the Chicxulub crater as well as a site in Texas and another in northeast Mexico show that the Chicxulub meteor hit the Earth 300,000 years before the mass extinction, said paleontologist Gerta Keller of Princeton University. Microscopic marine animals survived unscathed.

"The Chicxulub impact alone could not have caused the mass extinction because this impact predates the mass extinction," said Keller, who will present the research tomorrow at the Geological Society of America's annual meeting in Philadelphia. "We cannot attribute any specific extinctions to this impact."

Keller and colleagues from Switzerland and Germany believe it was the second, larger impact that left the layer of the metal iridium in rocks the world over and was the final blow for dinosaurs and other animals. Just where it struck, they don't know.

-- Christopher Lee

Darwin Evolves on the Web

Call it extreme evolution: Now you can read Charles Darwin's handwritten journals on the Internet, gaze upon digitized images of his original drawings and even listen to podcasts of his works.

Proving that the King of Evolution is still evolving, the University of Cambridge last week announced it is making Darwin's complete works available free on the Web, including 50,000 pages of searchable text and 40,000 images.

Much of the material (visible at http://www.darwin-online.org.uk ) has never been published before. It was compiled by project director John van Wyhe, who spent four years cajoling libraries and other sources around the world to contribute scans of their holdings. Most text pages are visible as both originals and as transcriptions in modern type.

But why stop there?

"There's no reason why, if you can search and read the text and look at images of the original, you shouldn't be able to download and listen to it as well," van Wyhe said. So with the help of text-recognition software, the material is also available as MP3 audio files that can be burned onto CDs or loaded onto iPods.

Listen up: "It may be said that natural selection is daily and hourly scrutinizing, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working."

Those were the man's words back in 1859, as he took pen to paper and began the work that he would eventually title "On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life."

Darwin recognized natural selection for the ruthless pruner it is. But so far, at least, his family has made the cut. The new Web site was introduced at a ceremony Friday featuring Randal Keynes -- Darwin's great-great-grandson.

-- Rick Weiss