axies. These stars run out of nuclear fuel and collapse into black holes, emitting prodigious amounts of energy in gamma rays, which are a very energetic version of X-rays.
For the short bursts, though, there was no evidence that this was the case. On the contrary, many theories have held that these bursts are produced by the collision of two small, compact objects - either two neutron stars, or one neutron star and a small black hole. In either case, a larger black hole is formed as the result of a collision.
Once the HETE-2 spacecraft pinpointed the source of the short burst, observers found for the first time a faint, short-lived optical afterglow, which represents the embers of the explosion that produced the burst. This, in turn, allowed astronomers to identify the galaxy in which the burst had occurred, and to measure its distance - which, by astronomical standards, was relatively small: just one billion light years from Earth instead of the usual10 billion light years for the long bursts.
- Robert Sanders
What was that you typed?
Berkeley computer scientists recently took sound recordings of users typing at a keyboard, fed the audio into a computer, and used an algorithm to recover up to 96 percent of the characters entered. "It's a form of acoustical spying that should raise red flags among computer-security and privacy experts," said Doug Tygar, professor of computer science and information management and principal investigator of the study.
Each keystroke makes a relatively distinct sound, however subtle, when hit. Typical users type about 300 characters per minute, leaving enough time for a computer to isolate the sounds of individual keystrokes and categorize the letters based upon the statistical characteristics of English text.
Using statistical learning theory, the computer can categorize the sounds of each key as it's struck and develop a good first guess, with an accuracy of 60 percent for characters and 20 percent for words. Spelling and grammar checks refine the results, increasing the character accuracy to 70 percent and the word accuracy to 50 percent. The recording is then played back repeatedly in a feedback loop to "train" the computer to increase its accuracy until no significant improvement is seen.