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发信人: Lg (创造人生的传奇), 信区: Linux
标 题: Parallel Computing Reveals Cosmic Riddles
发信站: BBS 荔园晨风站 (Mon Dec 6 09:55:54 1999), 站内信件
On Pablo Dmitruk's computer in UD's Sharp Laboratory, bright
white and
green circles converge and dance across the screen, then turn
yellow and
disappear.
"This shows what happens to gas in the solar atmosphere, or
corona, where it
heats up," explained Dmitruk, a research scientist with the
Bartol Research
Institute at UD. "Magnetic fields contribute to intense
turbulence, which
enhances energy dissipation, making the sun's corona much
hotter than its
surface."
To learn how coronal heating ultimately affects satellites in
space and life on
Earth, Bartol faculty member Bill Matthaeus said, computer
simulations are
essential. Studying activity on the sun's surface and in the
corona also provides
insights into the fundamental nature of space physics, plasma
and the universe,
according to Dmitruk.
"The sun is like a big laboratory for understanding plasma
properties, which
influence so many other events in space," Dmitruk added.
Unfortunately, questions about coronal heating and other
complex cosmic
problems can be tough or impossible to tackle with
single-processor
computers.
On Oct. 1, the National Science Foundation (NSF) awarded $500,
000 to
support a new parallel computing facility for Bartol. The
"major research
infrastructure" (MRI) grant will support a parallel system
based on 100 linked
processors, each of which will run at speeds up to 600
megahertz, connected
by fast Ethernet hardware, reported Matthaeus, who will serve
as principal
investigator for the project.
New equipment will support simulations in the fields of
astrophysics, space
sciences, condensed matter physics, turbulence theory, solar
physics and
more, Matthaeus said. With NSF funding available through Sept.
30, 2002,
Bartol/UD researchers are investigating a system similar to the
Avalon-Beowulf Cluster, developed by the Los Alamos Center for
Nonlinear
Studies and Goddard Space Flight Center. (See
http://cnls.lanl.gov/Internal/Computing/Avalon/.)
Bartol's latest award follows two other NSF grants in 1996 and
1997, which
paid for a complete modernization and expansion of the
institute's computing
facilities. The new NSF award "will give us a truly
world-class, parallel
computing facility," Matthaeus said. "It should be a
significant drawing card for
students and faculty."
To run parallel computing jobs, researchers from many campus
units--including Bartol, physics and astronomy, electrical and
computer
engineering (ECE), computer and information sciences (CIS) and
mechanical
engineering (ME)--must first develop suitable "code" or
instructions for the
machines, Matthaeus said. As part of his doctoral thesis work
in Argentina,
Dmitruk already has developed parallel code for the coronal
heating
simulation.
Simulations allow researchers to visualize and understand
events they
otherwise couldn't see because X-ray and white-light images
"tell us only part
of the story," Matthaeus said. "For example, there are no
diagnostics available
for detecting the small-scale, intense electric currents that
may be responsible
for heating the plasma to one- or two million degrees in the
lower corona."
And, coronal heating doesn't follow conventional rules: While
heat normally
dissipates as it moves outward, the sun's lower atmosphere is
much hotter
than its visible surface, the photosphere.
On the sun, Dmitruk explained, magnetic fields confine and
direct motions of
plasma, which consists of protons, electrons and ionized
particles.
Disturbances in the corona involve interactions of the plasma
and the magnetic
field. These motions can't always be observed, but they can be
accurately
calculated using computer models.
By comparing his computer simulation of those
disturbances--using a model
called reduced magnetohydrodynamic (RMHD)--with data from
observations
and mathematical calculations, Dmitruk can better assess
heating and energy
loss within different parts of the corona.
The bottomline, Dmitruk said, is that "all the mixing, or
disturbance in the sun's
surface and corona, triggers a very rapid energy loss." This
loss is
characterized by a cascade of energy at smaller and smaller
scales, where it is
efficiently dissipated, resulting in a turbulent state. "Now,"
he said, "we must
determine how that activity accelerates and controls the solar
wind, which
affects the protective bubble or magnetosphere around the
Earth."
The NSF grant will promote new knowledge of a host of cosmic
questions.
Those slated to use the parallel system include Gary Zank,
David Seckel, Stan
Owocki and Dermott Mullan of Bartol; Krzysztof Szalewicz,
physics and
astronomy; and Lori Pollock,CIS. Shiyi Chen, a former Bartol
student now
with Johns Hopkins University; and Sean Oughton, another
Bartol graduate
with University College, London, also will collaborate with
the UD/Bartol
team.
Additional UD collaborators include Guang Gao, ECE; Gagan
Agrawal and
David Saunders both of CIS; and Lian-Ping Wang, ME.
###
To view the coronal heating simulation, see
http://www.udel.edu/PR/NewsReleases/corona.html.
--
☆ 来源:．BBS 荔园晨风站 bbs.szu.edu.cn．[FROM: bbs@202.104.99.66]
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