Physics News Update, Number 478

Number 478, April 6, 2000 by Phillip F. Schewe and Ben Stein

AN ELECTRICAL CIRCUIT MIMICS YEN-DOLLAR FLUCTUATIONS. In one of the latest examples of econophysics (Update 395), Hideki Takayasu of the Sony Computer Science Laboratories in Japan (takayasu@csl.sony.co.jp) and his colleagues have designed an electrical circuit with voltage fluctuations that are highly similar to the fluctuations in a plot of the yen-dollar exchange rate. The Sony goal is to build a fast calculator for the prices of options which depend on exchange rates.

In the world of currency exchange, options serve as an insurance policy for a future exchange rate. Buying an option means that you have the right to purchase currency at some point in the future at a predetermined price, even if the actual exchange rate at the time is against your favor.

At the recent APS meeting in Minneapolis, Takayasu showed that graphs of yen-dollar fluctuations look remarkably similar at different time scales, suggesting a fractal behavior. The researchers then designed an inexpensive electrical circuit that produces highly similar fluctuations by employing naturally occurring electrical noise as the seeds for random variations. Their circuit costs approximately $5, and it can estimate yen-dollar fluctuations as fast as the $10,000 workstations that are running mathematical simulations of the exchange rates.

SUNSPOTS ON THE FAR SIDE OF THE SUN can be detected through helioseismic holography, a process in which the sound waves that rumble through the body of the sun are slightly distorted when they reflect from the magnetically active regions around sunspots. In March of 1998, data from the orbiting Solar Heliospheric Observatory (SOHO) were processed with an algorithm that deduces the locations of those out-of-sight sunspots. Charles Lindsey and Douglas Braun of the Solar Physics Research Corp. report that their calculations of presumed sunspot positions on the far side of the sun correlated well with actual spots that later swung into view (revolving along with the sun on its 27-day rotation).

The researchers expect that eventually this method will be able to give valuable advance warnings of the type of space storms that arise from the solar flares and coronal mass ejections associated with the active regions on the sun's surface. Predicting "space weather" in the Earth-sun environment is important since astronauts' lives, the survival of satellites, and the stable operation of terrestrial power grids are tied to the particles and radiation that comes rushing at us from the sun. (Lindsey and Braun, Science, 10 March 2000.)

THE MOST POWERFUL TRANSMISSION ELECTRON MICROSCOPE (TEM) has been built by a team led by Akira Tonomura at Hitachi's Advanced Research Lab. in collaboration with the Japan Science and Technology Corporation. In this kind of "field-emission" TEM, electrons are forced out of a cathode and accelerated with the use of a huge voltage and sent toward a sample. The voltage used was one million volts, and this produced a beam of electron waves with an intensity (more exactly, brightness) 4 times better than the best previous TEM (or 1000 times larger than conventional thermionic-emission TEMs).

The device is a marvel of engineering. The voltage has to be held steady at around a million volts with a stability of half a volt; while the electron source must be steady to within 0.5 nm. The new device can make out rows of atoms only half an angstrom apart (thus rivaling scanning tunneling microscopes) and can even take pictures fast enough, 60 per second (the same as TV), that movies have been made of fine gold particles changing their shapes.

Hitachi's Takeshi Kawasaki (tkawa@harl.hitachi.co.jp, 011-81-492-96-6111) says that the microscope will be useful for observing certain dynamic properties of condensed matter systems, one example being the movement of vortices in high-temperature superconductors. (Kawasaki et al., Applied Physics Letters, 6 March 2000; Select Article.)