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12 December 2013 1:00 pm ,
Vol. 342 ,
In an ambitious project to study 1000 years of sickness and health, researchers are excavating the graveyard of the now...
Stefan Behnisch has won awards for designing science labs and other buildings that are smart, sustainable, and...
The iconic 125-year-old Lick Observatory on Mount Hamilton near San Jose, California, is facing the threat of closure...
Recent results from the Curiosity Mars rover have helped scientists formulate a plan for the next phase of its mission...
A new, remarkably powerful drug that cripples the hepatitis C virus (HCV) came to market last week, but it sells for $...
In pretoothbrush populations, gumlines would often be marred by a thick, visible crust of calcium phosphate, food...
Evolutionary biologists have long studied how the Mexican tetra, a drab fish that lives in rivers and creeks but has...
Victorian astronomers spent countless hours laboriously charting the positions of stars in the sky. Such sky mapping,...
- 12 December 2013 1:00 pm , Vol. 342 , #6164
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How to Outsmart a Video Pirate
10 December 2008 (All day)
Researchers have developed a dirt-cheap and simple way to expose bootleg CDs and DVDs. The approach is so easy, in fact, that anyone with a laser pointer can do it.
You can't always tell a disc by its back cover. Commercial and pirated CDs and DVDs look nearly identical to the eye, even though commercial products are manufactured in large quantities via a hydraulic press and a master recording, and bootlegged versions are burned, one at a time, with a laser. Up until now it has taken an expert's eye or special equipment to detect whether, say, a DVD of Spider Man 3 is the legitimate article or a knockoff.
Five optical physicists at Spain's University of Grenada think they have found an easier way. The key is structural differences between commercial and writable disks, and how those differences affect the way light waves bend around them--a process called diffraction. Commercial disks contain microscopic pits overlain with clear plastic material; a disc player's laser reads the changes in surface elevation as audio or video signals or both. Writable disks, meanwhile, contain a compound into which a recording laser can burn tiny marks that are read by a disc player--hence the term "burning" a disc. Shine a laser--even a standard laser pointer--on both, and the difference becomes clear, the team reports. On a manufactured disc, the reflected beam shows up as a small dot on a white surface. On a copy, however, the dot is larger and is accompanied by two parallel lines above and below it (see picture).
In this month's issue of the American Journal of Physics, the researchers describe testing their technique on more than 100 CDs and DVDs of various labels with different types of content. The method "is completely reliable," says co-author Javier Hernández-Andrés.
Optical physicist Chunlei Guo of the University of Rochester in New York state agrees and says and the finding should aid efforts to detect CD piracy. It's also a great way to teach students the concept of diffraction, he says, something that is difficult to spot in everyday life.