SCIENCE
Notebook
Monday, October 23, 2006; Page A08
'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."
  Charles Darwin's works will be placed on the Internet free, courtesy of a Cambridge project. (National Museum Of Natural History) |
"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.
