Number 111, January 21, 1993 by Phillip F. Schewe and Ben Stein
SQUID DETECTORS OPERATING IN THE MILLIATTOVOLT range have been able
to measure a tiny resistance in a YBaCuO thin-film superconductor, even
in low magnetic fields and for low currents (F.C. Wellstood et al., 4 Jan.
1993 Physical Review Letters). The resistance arises from noise in magnetic
flux lines which do seem to penetrate the sample even though the external
fields used are far below the critical field at which penetration is supposed
to commence. By the way, although the scientists in this Maryland-AT&T-Berkeley
collaboration use the prefix milli-atto to denote 10 raised to the -21st
power, the official name for this prefix is "zepto," or just
z. For those who would go further yet, the name for 10**-24 is "yocto."
(Science News, 16 Jan. 1993.)
CHANGES IN THE EARTH'S ROTATION RATE occur at the level of several parts
in 10**8. Using laser ranging (bouncing radar waves off the Moon or satellites)
and very long baseline interferometry, length-of-day (LOD) measurements
can detect 0.03 msec changes. Jean Dickey, a JPL geophysicist, cites three
main types of LOD change: a linear increase owing to tidal dissipation;
larger, irregular variations, on the scale of decades, owing to core-mantle
interactions; and shorter-term (seasonal) changes from the angular momentum
exchange between crust and atmosphere. (Eos, 12 Jan. 1993.)
HOW ELEMENTARY PARTICLES COME TO HAVE THE MASS THEY DO is "the
most important outstanding problem in particle physics today," says
Berkeley scientist Lawrence Hall. The standard model is not much help:
indeed, certain of the known particle masses are used as input parameters
for the theory. Hall and his colleagues Savos Dimopoulos of Stanford and
Stuart Raby of Ohio State have advanced a new model, reworking parts of
the existing theories, which makes six specific testable predictions (Phys.
Rev. Lett., 30 Mar. 1992) on such topics as B-meson decay, proton decay,
and the top quark (their estimate for the mass: 188 GeV). The top is being
pursued at Fermilab and new proton-decay experiments are being readied
in Japan---the Super Kamiokande detector---and Italy---the Icarus detector.
(Science, 8 Jan. 1993.)
BRIGHTNESS VARIATIONS IN SUN-LIKE STARS were as large as 2.7% for a
sample of 33 stars studied over eight years. The average year-to-year brightness
variation for those stars similar to the Sun in age was 0.16% (rms), compared
with 0.04% for the Sun. The scientists who made the photometry observations
of the stars at the Lowell Observatory conclude (contact Sallie Baliunas,
Smithsonian Astrophysical Observatory, 617-495-7415) that although the
Sun is in an unusually steady phase right now, eras of larger-amplitude
variability, such as the Maunder Minimum (AD 1645-1715), may occur more
often than previously believed and that reconstructions of past solar brightness
should take this into account. (Nature, 17 Dec. 1992.)
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