Richard A. Lovettfor National Geographic News
May 6, 2009
{Cloaking devices, like the Star Trek technology that can make whole Romulan warships disappear, came a step closer to reality last week.
Two independent teams have developed silicon-based materials that can hide microscopic objects. The materials are the first to work in near-infrared light, wavelengths very close to visible light.
On a flat surface, an object covered with a piece of cloth would normally be detectable based on its telltale bump. But with the new materials, even the bump seems to vanish.
A team led by Xiang Zhang at the University of California, Berkeley, achieved this effect by drilling scores of tiny nano-holes into the cloaking material.
(See pictures of materials that use nanotechnology.)
These holes change the material's optical properties, allowing light to bend around the hidden object, as described in the April 29 issue of Nature Materials.
The other team, led by Michal Lipson at Cornell University, achieved the same effect by covering their material's surface with tiny pillars also designed to bend light. The Cornell group's paper is currently under review by Nature Photonics.
Jason Valentine, one of the Berkeley researchers, calls his team's material a "carpet cloak." In both cases the process is like hiding something beneath a rug.
"The object is effectively hidden on the ground," Valentine said.
Small But Effective
Both materials still have a long way to go before they're ready for stealth military operations. To start with, both cloaks work only in infrared light for now. The next step is to try to develop a version that works in visible wavelengths.
The cloaks are also capable of hiding only microscopic objects.}
http://news.nationalgeographic.com/news/2009/05/090506-cloaking-device-star-trek.html
{But even that has potential uses, Valentine said. In optical computing, for example, such cloaks could be used to allow light to move more efficiently, by hiding the parts of a computer chip that get in the way of the beams.
Also, expensive dielectric mirrors—special mirrors used to make printed circuits for electronics—can be ruined by tiny defects in their surfaces.
"You could cloak a defect and make it look like a perfect mirror again," Valentine said.
Scaling up to hide an object the size of a BB-gun pellet might be possible, but going larger will be difficult, he said.
In the Berkeley material, for instance, "the holes have to be smaller than the wavelength of light, and many are required."
From Theory to Practice
The development of these working invisibility cloaks is exciting, but it's not a huge theoretical breakthrough, Ulf Leonhardt, a theoretical physicist at Scotland's University of St. Andrews, said in an email.
"Such an idea already appeared in my very first paper on cloaking," published in the journal Science in 2006, he said.
(Read "Invisibility Cloaks Possible, Study Says.")
Carl Poitras, a researcher with the Cornell group, agrees.
"Like a lot of things we can do," he said, "the theory is predicted ahead of time, but the technology isn't there to show it."
Now, for cloaking devices at least, the theoretical models are starting to become real-life products.}
http://news.nationalgeographic.com/news/2009/05/090506-cloaking-device-star-trek_2.html
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Invisibility Cloaks Possible, Study Says
Sean Markeyfor National Geographic News
May 25, 2006
http://news.nationalgeographic.com/news/2006/05/060525-invisibile.html
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Invisibility Shields Planned by Engineers
James Owen in Londonfor National Geographic News
February 28, 2005
http://news.nationalgeographic.com/news/2005/02/0228_050228_invisibility.html
Friday, May 8, 2009
Friday, May 1, 2009
The PATH and BART
http://en.wikipedia.org/wiki/Hudson_Terminal#Hudson_Terminal http://www.nytimes.com/slideshow/2008/10/27/nyregion/20081027_TUNNEL_SLIDESHOW_3.html
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Although SF isn't an island like Manhattan is, the SF Bay needed an underwater BART tunnel as much as NY&NJ needed its PATH tunnels under the Hudson River.
While the forerunner of PATH was up & running by 1908, BART didn't start until 1974.
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{BART began regular passenger service on September 11, 1972, reporting more than 100,000 passengers in its first five days of operations.} http://en.wikipedia.org/wiki/History_of_the_Bay_Area_Rapid_Transit#Operation
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As BART opened on September 11, the M2 part of the Istanbul Metro commenced on that date.
{Construction of the Istanbul Metro, also known as the M2, began on September 11, 1992, but faced many challenges due to the numerous archaeological sites that were discovered during the drilling process, which slowed down or fully stopped the construction of many stations. Taking into account the seismic activity in Istanbul, the entire subway network was built with the cut-and-cover method to withstand an earthquake of up to 9.0 on the Richter magnitude scale.}
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The Marmaray Tunnel is on the scale of the BART Transbay_Tube.
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