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On Tech Brief today: Murder inside Twitter and a helmet that cares.

• Beware, the posters are watching. Well, some of them. In 27 subway stations in Tokyo. :

"'The camera can distinguish a person's sex and approximate age, even if the person only walks by in front of the display, at least if he or she looks at the screen for a second,'" said a spokesman for the project. If data for different locations is analysed, companies can provide interactive advertisements 'which meet the interest of people who use the station at a certain time,'

• When you were young, your parents were the ones that warned you to be careful when playing outside and took you to the hospital when your exuberance outran your physical prowess. Now you are all grown up, who is going to keep an eye on you? If you are a skier or snowboarder, the :

"The team designed a traditional ski/snowboard helmet lined with sensors that measure acceleration. An accompanying LCD screen displayed colors whenever the helmet experienced an impact. If the impact was mild, the screen would display a green color. If the impact was severe, the screen would display red."

In the event of a bad fall, the helmet could call for first aid and alert rescuers to an injured person's location. Even with light knocks, it could be a boon:

"The helmet could serve as an important innovation because of the complex nature of head injuries. Though many folks knock their heads while skiing or engaging in other sports, not everyone seeks medical attention for these seemingly mild injuries. According to the Northeastern team's research, if seemingly mild head injuries are left untreated, they can actually become more serious than a concussion."

• If a robot were given some of your memories and made to look like you, how convincing would it be? Could you take the day off while the replicant filled in? :

"It can make eye contact, and even recognize faces it knows (to some degree). Using an Internet connection it can get some deeper information to answer questions, and it's likely that it occasionally draws on Bina Rothblatt's data for some of its personality and desires (does the real Bina like to garden?). Yet its conversation skills seem no better than those chatbots that aren't based on real people."

• Micro-blogging site Twitter has given a peep behind the scenes at the string, sealing wax and mice on wheels it uses to keep the service rolling. Lately, it has been looking into ways of speeding up the way it updates its server farms. The solution? .

"It was time for something completely different, something decentralized, something more like.. BitTorrent... running inside of our datacenter to quickly copy files around. Using the file-sharing protocol, we launched a side-project called Murder and after a few days (and especially nights) of nervous full-site tinkering, it turned a 40 minute deploy process into one that lasted just 12 seconds!"

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