Research
Penn State Intercom......August 30, 2001

Technique will control
electron spin

Researchers from the University of California at Santa Barbara and Penn State have revealed an ability to quickly manipulate electron spins that could positively impact the development of items such as quantum computers.

The experiments are the result of a long-standing collaboration between David Awschalom at UCSB and Nitin Samarth at the University.

The research suggests an ability to quickly manipulate electron spins by loosening the stringent requirements of coherence times. While previous research has been aimed at increasing the coherence time of electron spin in semiconductor quantum structures, the experiments present an alternate approach. In effect, the researchers have discovered a technique that can potentially circumvent the otherwise stringent constraint of the electron spin coherence time in solid-state materials. The use of ultra-fast laser pulses to manipulate spins would represent a speed-up of the process by 100,000 times when compared with conventional methods, and opens new directions for research into solid-state implementation of quantum computers.

For the full story, go to http://www.science.psu.edu/alert/Samarth6-2001-2.htm

Fault lines may not
move equal distances

By A'ndrea Elyse Messer
Public Information

While most scientists assume that both sides of a geologic fault move equal distances during an earthquake, University researchers have discovered that not all strike slip faults act that way.

"In the past, no one looked at the contrast between the two sides of a strike slip fault," said Kevin P. Furlong, professor of geosciences. "These faults have always been modeled as if both sides were equal by definition."

Furlong, along with Rocco Malservisi, a doctoral degree student in geosciences; and Timothy H. Dixon of University of Miami, investigated the Eastern California Shear Zone, a strike slip fault system running parallel to the San Andreas fault about 150 miles east of San Francisco. The area, on the Nevada/California border, is the eastern edge of the interface of the Pacific and North American plate boundaries and is linked to the San Andreas fault. In a strike slip fault, the ground on each side of the fault moves along the fault line, but in opposite directions.

The western side of the fault, consisting of the Sierra Nevada Mountains, and the eastern side of the fault, that of the Basin and Range, have very different heat flow properties, which the researchers believe is the cause of the contrast between the two sides.

According to the researchers, the colder Sierra Nevada side acts like a solid block, recovering fairly quickly from an earthquake, while the warmer, more viscous Basin and Range side deforms more like rubber. When an earthquake occurs, the Sierra Nevada side only needs to snap back a small distance, while the Basin and Range side rebounds much more and then continues to recover for a much longer time.

Furlong, Malservisi and Dixon reported on their on-site study of this fault. Using permanent location markers and Geographic Positioning System equipment, they were able to record the difference in movement on each side down to about 1 millimeter. They found a difference of a half to three-quarters of an inch a year on the rigid side out of a total movement along the fault of 3 inches.

"Before the accuracy of G.P.S. became so good, it was impossible to do this kind of research," Furlong said. "We could not have seen the difference before."

If the researchers' results hold true, their approach could be applicable in many places. While local geography can cloud the existence of true contrasts across sides of a fault, there are hints of this asymmetry occurring in other places. Satellite images of a 1997 earthquake in Tibet show that the earthquake occurred more on one side of the fault than the other. The area is so remote, however, that it is not currently possible to determine if subsurface differences are the cause.

A'ndrea Elyse Messer can be reached at aem1@psu.edu.

Shark attacks follow
theory of probability

A University expert on probabilistic simulation thinks that the large number of shark attacks that recently took place in Florida and the Bahamas might be explained through probability theory.

"It really does seem that there is indeed something odd going on with the ocean currents, temperatures, food supply, or water chemistry, which would explain the recent reported spate of shark attacks; however, even if such attacks were purely 'random' and independent of each other, it is not surprising that they seem to occur in 'clumps' in time -- like this past summer -- and then not at all for a long time," explained David Kelton, professor of management science in The Smeal College of Business Administration.

Kelton, who researches the probabilistic and statistical aspects of simulation, is chair of the Department of Management Science and Information Systems.

"There is something in probability theory called a Poisson process, giving amazingly good descriptions of such random independent events occurring through time, like customer arrivals to a fast-food store, cosmic rays striking a planet, accidents in a factory, airplane mishaps, and, maybe, shark attacks," Kelton said.

Reasonable and realistic physical assumptions imply that the time between successive events follows what is called an exponential distribution, the most likely value of which is zero (or arbitrarily close to zero).

"So on a time line, you see lots of very small inter-event times, meaning that the events happen in clumps, then a long time will go by when nothing happens, representing an infrequent but possible observation from the right tail of the distribution," Kelton said. "After the fact, it seems that 'it never rains but when it does, it pours.' This is what's sometimes called a 'Poisson burst' of events."

This process, Kelton points out, was discovered by the French mathematician and probabilist Poisson, who was consulting with the Prussian army to explain why so may Prussian army officers were being killed by getting kicked by horses.

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