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Social networks are rife with examples of users failing to understand the privacy implications of posting sensitive information online.
In February, for example, school officials in Wisconsin suspended a teacher who posted on Facebook a picture of herself pointing a gun at the camera. In April, the Swiss insurance company Nationale Suisse fired an employee after she called in sick and then posted updates on the same site. Others have raised concerns about users handing so much personal information to social-networking companies themselves.
Now, researchers at the University of Waterloo in Ontario have developed a browser plug-in to help users keep their information private from prying eyes and from social-network providers as well. Urs Hengartner, an assistant professor of computer science, and his colleagues say the plug-in replaces sensitive information in a user’s profile and news feed with meaningless text that can only be unscrambled by trusted friends or contacts. Dubbed FaceCloak, the tool assures its users that sensitive data stays private, Hengartner says. “If you have a particular illness, you might want to allow only your friends to see that,” he says. “This leaves it up to the user to decide what information to keep away from Facebook.”
The tool is the latest shot in a battle between social networks and privacy-conscious users. Most users of Facebook, MySpace, and other social networks remain unaware of the privacy implications of posting personal information to such sites, says Alessandro Acquisti, an associate professor of information systems and public policy at Carnegie Mellon University.
Today’s solar cells lose much of the energy in light to heat. Now researchers at Cornell University have made a photovoltaic cell out of a single carbon nanotube that can take advantage of more of the energy in light than conventional photovoltaics. The tiny carbon tubes might eventually be used to make more-efficient next-generation solar cells.
“The main limiting factor in a solar cell is that when you absorb a high-energy photon, you lose energy to heat, and there’s no way to recover it,” says Matthew Beard, a senior scientist at the National Renewable Energy Laboratory in Golden, CO. Loss of energy to heat limits the efficiency of the best solar cells to about 33 percent. “The material that can convert at a much higher efficiency will be a game-changer,” says Beard.
Researchers led by Paul McEuen, professor of physics at Cornell, began by putting a single nanotube in a circuit and giving it three electrical contacts called gates, one at each end and one underneath. They used the gates to apply a voltage across the nanotube, then illuminated it with light. When a photon hits the nanotube, it transfers some of its energy to an electron, which can then flow through the circuit off the nanotube. This one-photon, one-electron process is what normally happens in a solar cell. What’s unusual about the nanotube cell, says McEuen, is what happens when you put in what he calls “a big photon” — a photon whose energy is twice as big as the energy normally required to get an electron off the cell. In conventional cells, this is the energy that’s lost as heat. In the nanotube device, it kicks a second electron into the circuit. The work was described last week in the journal Science.
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