From: LARRY KLAES (ljk4_at_msn.com)
Date: Thu Feb 06 2003 - 09:49:34 PST
----- Original Message -----
From: physnews_at_aip.org
Sent: Thursday, February 06, 2003 12:14 PM
To: ljk4_at_MSN.COM
Subject: Physics News Update 623
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 623 February 5, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon
NEW SUPERBURST THEORY. When a neutron star pulls matter from a nearby
companion onto itself, powerful x-ray bursts, visible to telescopes in Earth
orbit, can result. Some astronomers believe the bursts leave behind an
ocean of debris, heavy nuclei mostly, on the neutron star's surface.
Occasionally much larger "superbursts," with up to 1000 times the amount of
x rays than other bursts, can flare up. Henrik Schatz of Michigan State
University (schatz_at_nscl.msu.edu, 517-333-6397) and his collaborators Lars
Bildsten from UCSB and Andrew C-u-m-m-i-n-g of UCSC believe that an energy
blitz is generated when high energy photons strike the heavy nuclei in the
debris ocean, springing free either a proton, neutron, or alpha particle,
which then recombine with the residual nuclei forming lighter, stronger
bound nuclei and free energy. This photodisintegration process is triggered
by the thermonuclear explosion of a small amount of carbon, but may then
proceed subject to positive feedback: the warmer the surface temperature the
more disintegration, which in turn leads to warmer temperatures. The
runaway production of energy through the conversion of heavy nuclei into
lighter nuclei could be unique in astrophysics: all other thermonuclear
energy generation (such as those inside our sun) proceeds by fusing lighter
nuclei into heavier nuclei. (Upcoming article in Astrophysical Journal
Letters; see also http://groups.nscl.msu.edu/nero/ )
LORENTZ VIOLATIONS? NOT YET. Lorentz invariance, the idea that the
result of a physics experiment should stay the same whether the apparatus is
motionless or traveling at some great constant speed relative to a reference
point, is taken for granted in the theory of special relativity. Yet in
recent years some scientists have come to question this pillar of physics,
and to suggest theoretical models (called "standard model extensions," or
SMEs ) incorporating Lorentz violations and experimental ways of settling
the matter (see Update 578, www.aip.org/enews/physnews/2002/split/578-2.html
). In these models, the speed of light is not universal but will have
extra terms dependent on the speed or orientation of the apparatus (see
http://media4.physics.indiana.edu/~kostelec/faq.html ).
Even before the advent of Einstein's relativity, the Michelson-Morley
experiment tried to perceive (unsuccessfully) a difference in the speed of
light when the Earth was traveling in two different directions in space
while on opposite sides of its orbit around the sun. Now scientists
have to be more subtle in their approach. In one new laboratory
experiment, just completed by Stanford physicists (John Lipa, 650-723-4562,
john.lipa_at_stanford.edu ) microwaves in two resonant cavities (one
oriented east-west, the other pointing vertically) are monitored as the
Earth sweeps around the sun. Any orientation- or speed-dependent changes in
the speed of light would alter the resonant conditions of the cavities in a
measurable way. The geometry of the experiment gives it optimal sensitivity
to a number of coefficients in a generalized SME. The Stanford group sees
no such anisotropy at the level of 10^-13 for velocity-independent terms,
and at the 10^-9 level for velocity-dependent terms. (Lipa et al., Physical
Review Letters, upcoming article; text at www.aip.org/physnews/select )
GROUND TEMPERATURES SINCE THE YEAR 1500 can be read back by examining the
temperatures in deep boreholes. Temperatures in the Earth's crust are
determined by a combination of surface climate effects and internal heat
flow. The general trend is a linear rise in temperature with depth, but
this is modulated by heat perturbations which act in a nonlinear way;
typically perturbations penetrate about 20 meters of depth per year or about
150 m in 100 years. Hugo Beltrami (St. Francis Xavier University in Nova
Scotia) has examined temperature-depth profiles from 826 places around the
world. Taking into account the known temperature anomalies, he is able to
work out the average surface energy flux and temperature for many localities
and for the world as a whole back for a period of 500 years. Beltrami
(902-867-2326, hugo_at_stfx.ca) finds that global average surface temperature
has increased by 0.45 K in the last 200 years. During this time, however,
some places have experienced more dramatic average temperature swings: for
example, parts of Africa show a cooling while northern Canada is warmer (3-4
K) during the same period. (Geophysical Research Letters, vol 29, 23, 2111;
also see http://geophysics.stfx.ca/public/index.html )
***********
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