Number 201, November 3, 1994 by Phillip F. Schewe and Ben Stein
VERY ENERGETIC COSMIC RAYS are scarce. Studies over many years indicate
a decided dropoff at energies above 10**20 eV. Previously only two definite
cosmic-ray events at this energy had been recorded. Now a third---with
an energy of 1.7-2.6 x 10**20 eV---has been recorded, at the Akeno Giant
Air Shower Array (AGASA) in Japan. Astronomers there suspect that the cosmic
ray originated outside our galaxy but could not have traveled more than
about 100 million light years owing to the energy that would be lost to
the universal background radiation en route. The AGASA detector, which
samples the shower of particles engendered by the cosmic-ray particle in
the upper atmosphere, could determine the incoming angle to within one
degree on the sky. Taking into account the effect of the intergalactic
magnetic field, the cosmic ray's starting point was assigned to a location
at the edge of the Pisces galaxy cluster, a place where no active galactic
nucleus (a likely engine for so powerful a cosmic ray) is known to reside.
(N. Hayashida et al., Physical Review Letters.)
MAGNETIC VORTEX LINES ARE INDEED LINES . The expected commercial use
of ceramic superconductors in high-field magnets encourages scientists
to find out what happens to the magnetic flux lines (from an external magnet)
once they organize themselves into bundles as they penetrate the surface
of a superconductor sample. If the magnetic field is too strong or if a
current moving through the sample is too large, the flux lines inside the
sample might begin to move about, causing a resistive dissipation of energy,
defeating the whole reason for using superconducting materials if the first
place. A new experiment at Harvard demonstrates that the vortex lines persist
as relatively straight lines right through to the other side of the sample,
and do not splay out into pancake shapes as some theorists had feared.
The Harvard scientists used tiny magnetic particles to image the patterns
of vortices at the top and bottom of the sample. They then deduced a correlation
between the patterns. This information about the vortex geometry should
aid in the attempt to preserve the superconducting state in the sample
by pinning the vortex lines in place. (Zhen Yao et al., Nature, 27 October
1994.)
THE WORLD'S LARGEST SCALE MODEL OF THE SOLAR SYSTEM begins in Peoria,
Illinois at the Lakeview Museum. In this model (where 42 ft=1 million miles)
the sun is painted on the 36 ft.-diameter dome of the museum's planetarium.
Mercury (1.5 in. diameter) is at a nearby store, Venus sits in a bank lobby,
and Earth (4 in. diameter) is lodged at a gas station. The rest of the
solar system is positioned as follows: Mars is at a radio station; Jupiter
(3 ft., 9 in.) is four miles from the sun at the Peoria Public Library;
Saturn (90 in. including the rings) is at the local airport; Uranus 15
miles distant rests at a school in the town of Pekin; Neptune 23 miles
away in Roanoke at a Dodge dealership; and Pluto 40 miles away from the
sun at a furniture store in Kewanee, Illinois. Affiliated with the scheme
are a number of comets and asteroids in places such as Evansville, IN,
Bowling Green, OH, and, further afield yet, in Ecuador, Chile, and Russia.
(For more information, contact Sheldon Shafer at 309-686-7000.)
|
