Professor Charles Horowitz of the IU Physics Department and the
Nuclear Theory Center carries out theoretical studies of dense
nuclear matter, with the aim of understanding Type II supernovas,
and the properties of neutron stars. Matter in these extreme
astrophysical phenomena can reach almost unimaginable densities,
beyond a trillion grams per cubic centimeter. At this density, atoms
are completely ionized. At yet higher densities, the ions themselves
lose their identities and turn into a soup of neutrons and protons.

Yet even at these high densities, matter can still be studied with a
semi-classical model very similar to the kind used to study simple
liquids. Simple liquids are modeled by assuming each atom exerts a
central force on all the rest. The motion of each atom is found by
simply integrating Newton's law, F=ma. In a molecular dynamics (MD)
simulation, time is broken up into a series of small intervals. At
the beginning of each time interval, all the forces are computed,
and the corresponding accelerations are integrated to update the
velocity and position of each particle.

The same type of thing can be done for the astrophysical situation.
The most time consuming part of a molecular dynamics simulation is
calculating all the forces. For a system of N particles, it takes
on order of N squared calculations to get all the forces, and a
physically realistic simulation may require anywhere from 10,000 to
100,000 particles. This means 100 million to 10 billion force
calculations per time step. Moreover, tens of thousands to millions
of time steps must be carried out to do a complete simulation, and
many such simulations may be necessary to properly explore the
physics.

Professor Horowitz's molecular dynamics simulations are a perfect
fit for a special purpose computer called the MDGRAPE-2, of which
IU has four. The MDGRAPE-2 performs the central force calculations
in special hardware that does only that type of calculation, but
does it as much as 50 to 60 times faster than a general purpose
computer. With the help of IU's four MDGRAPE-2 machines, he has
been able to carry out MD studies of supernova and neutron star
matter that would have taken years on a serial machine. The High
Performance Applications team has participated in this effort for
several years.

UPDATE: Time and Place MOVED!

The Research Technologies Round Table is moving to the last Thursday
of the month, to conflict less with other recurring events.

Thursday, January 31st, 12:30-1:30
ICTC 497 and IMU Sassafrass Room
Research Technologies Round Table

Randy Heiland, manager of the High Performance Applications group
[formerly HPC], will present an overview of their activities and
welcome questions from the audience. The mission of the HPA group is
to help promote scholarly research through the use of high
performance computing and communication environments. The HPA group
works closely with the High Performance Systems (HPS) group to
fulfill this mission. A sampling of HPA activities include: user
support for IU faculty, staff and students who want to get started
using our supercomputers, longer term 1-on-1 consulting, support
for our NSF TeraGrid users, benchmarking new or upgraded systems,
and (in the future) developing services that hide the complexity of
using high performance applications.