05 October 2005
Laser amplifier slows light at room temperature
A research team led by Connie Chang-Hasnain, professor of electrical engineering and computer sciences, has created a device that uses a laser amplifier to slow the speed of light more than one-million-fold. Building upon work completed one year ago in which researchers slowed light by a factor of 31,000 times, or 6 miles per second, the team clocked the speed of light at 245 meters per second, or three-quarters the speed of sound in air. Moreover, they did this at room temperature; last year's success required temperatures as low as 10 degrees Kelvin.
In optoelectronics, adjusting the speed of light is part of an effort to overcome a bottleneck in optical communications. Optical signals speed along fiber networks, but are then jammed as they hit an intersection, or router. At these intersections, light signals are converted to slower-moving electronic data to be directed to the correct path before being switched back to light, a process known as optical-electronic-optical (OEO) conversion.
The researchers hope eventually to freeze light in its tracks, which would open doors to a world of optical memory and storage.
- Sarah Yang
Health survey suggests extending insurance benefits to parents
Extending health insurance for low-income children to their parents may help improve these children's access to a regular source of care as well as reduce perceived discrimination and breaks in coverage, according to a new study by professor of maternal and child health Sylvia Guendelman and other Berkeley researchers.
The findings come three years after California legislators approved the expansion of Healthy Families, the state's public-health-insurance program for those 18 and under, to parents of eligible children. The expansion was never implemented, due to lack of funding.
Using data from the 2001 California Health Interview Survey, the researchers analyzed the responses from 5,521 low-income parents whose children were eligible for public health insurance. Not surprisingly, they found that children in families with no health coverage had higher odds of lacking a usual source of care, of not having seen a dentist within the previous two years, and of not seeing a doctor within the previous year, compared with children with child-only insurance and with children with an insured parent.
When comparing children in family coverage and child-only coverage groups, the researchers found that those in child-only coverage families were more likely to experience breaks in insurance coverage in the past year, to lack a usual source of care, and to perceive discrimination when receiving care.
"Those with child-only coverage tend to be kids from immigrant, predominantly Latino, families who seek care in the public sector," said Guendelman. "The public sector may be more overburdened and less available to offer care to these families, which may also have fewer resources to navigate the health-care system."
Solving the mystery of short gamma-ray bursts
An international team of scientists has obtained the best evidence yet that short-duration gamma-ray bursts are caused by the collision of two compact stars. The team, which includes Kevin Hurley, senior space fellow at Berkeley's Space Sciences Laboratory, will announce its results in the Oct. 6 issue of the journal Nature.
The breakthrough burst came on July 9 from the constellation of Grus (the crane) in the southern sky, and lasted only one-tenth of a second. The burst was captured by HETE-2, a spacecraft launched in 2000 by an international collaboration involving the United States, Japan, France, and other partners.
"That was the clue we were waiting for," said Garrett Jernigan, a research physicist at the laboratory. "Bursts seem to come mainly in two varieties - the long ones, which last about 20 seconds, and the short ones, which last a few tenths of a second. It's the short ones that have been puzzling us."
Evidence has mounted over the years that the longer bursts are caused by the collapse of massive stars in distant galaxies. 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.