By Barbara A. Hale
Public Information
An engineering professor said low-cost personal computers linked to form systems with supercomputer-like capabilities -- popularly known as Beowulf clusters -- can be a faster, cheaper alternative for many chemists, physicists, aeronautical engineers, electrical engineers and others who now have to wait to use machines at national supercomputer centers.
"Lots of the people who are using supercomputer centers are running only 16 processors at a time. They may find it more convenient to use these kinds of clusters and to leave the supercomputers to those who need 200 or more processors," said Lyle Long, professor of aerospace engineering.
"There are some very important scientific questions that can be tackled using relatively small-scale molecular dynamics, Monte Carlo, integral methods, or finite differences codes. However, one often needs to run these codes repeatedly to either build up statistical data or vary input parameters. One can very easily use the Message Passing Interface (MPI) paradigm, which is free and can be downloaded from the Internet, combined with the Fortran or C programming languages, to run thousands of different cases in a very short amount of time."
Long ran the examples on Penn State's COCOA, the COst effective COmputing Array, a 50-processor cluster of off-the-shelf PCs connected via fast Ethernet. The system, built to study complex fluid dynamics, has 13 gigabytes of RAM memory and 100 gigabytes of disk space. It cost about $100,000 in 1998 and would cost about half of that today. A supercomputer of similar power would cost about $750,000. Details on COCOA are at http://cocoa.aero.psu.edu/
"One of the real benefits of inexpensive machines is that they do not have to be shared with hundreds of other users, and we do not have to wait days in a queuing system," Long said. "We quite often have to wait hours or days at a supercomputer center just to use a few processors. In addition, while it is quite difficult to get 50,000 CPU hours at a supercomputer center, the COCOA Beowulf cluster provides more than 400,000 CPU hours per year. Furthermore, processors on parallel supercomputers are usually, at most, twice as fast as these PC processors for large production codes."
Long, who worked with Kenneth S. Brentner, senior research engineer in the computational modeling and simulation branch at NASA Langley Research Center in Hampton, Va., sees a trend to Beowulf clusters.
"We're already working on our next cluster. The price just falls every year," he said.
NASA News Service
Two
images made by NASA's Chandra X-ray Observatory, one in October 1999, the other
in January, show for the first time the full impact of the actual blast wave
from Supernova 1987A (SN1987A). The observations are the first time that X-rays
from a shock wave have been imaged at such an early stage of a supernova explosion.
Recent observations of SN 1987A with the Hubble Space Telescope revealed gradually brightening hot spots from a ring of matter ejected by the star thousands of years before it exploded. Chandra's X-ray images show the cause for this brightening ring. A shock wave is smashing into portions of the ring at a speed of 10 million miles per hour (4,500 kilometers per second). The gas behind the shock wave has a temperature of about 10 million degrees Celsius, and is visible only with an X-ray telescope.
"With Hubble we heard the whistle from the oncoming train," said David Burrows, professor of astronomy and astrophysics at Penn State, the leader of the team of scientists involved in analyzing the Chandra data on SN 1987A. "Now, with Chandra, we can see the train."
The X-ray observations appear to confirm the general outlines of a model developed by team member Richard McCray of the University of Colorado, Boulder, and others, which holds that a shock wave has been moving out ahead of the debris expelled by the explosion. As this shock wave collides with material outside the ring, it heats it to millions of degrees.
"We are witnessing the birth of a supernova remnant for the first time," McCray said.
Other members of the team were Gordon Garmire, Evan Pugh professor of astronomy and astrophysics, and John Nousek, professor of astronomy and astrophysics at Penn State; Eli Michael of the University of Colorado; and Una Hwang, Steven Holt and Rob Petre of NASA's Goddard Space Flight Center in Greenbelt, Md.
To see X-ray images captured by Chandra
or for information on Chandra's progress, check the
Web at http://chandra.nasa.gov/
or http://chandra.harvard.edu/.
By Paul A. Blaum
Public Information
Even
in the most open and democratic of workplace environments, employees tend to
find negative politeness the best way to broach a potential touchy subject with
superiors and co-workers, according to a study.
"Negative politeness seeks to minimize the sense of infringement implied in making a request, even when the request is justified or even necessary. This tactic also recognizes or establishes social distance between speaker and hearer," said David A. Morand, associate professor of management at Penn State Harrisburg.
"Apologetic language such as 'Excuse me,' 'Pardon me' and 'Sorry to bother you, but ...' acknowledge intrusion into the psychological territories of the other," said Morand. "Verbal hedges enable speakers to distance themselves from their own request. A third example of negative politeness is the use of honorific terms (Dr., Professor, Ms.), which elevates the hearer's status, thereby creating an aura of respect and social distance. This in turn cushions the impact of a request entailing possible loss of face on the part of either speaker or listener," Morand said.
Negative politeness is distinguished from positive politeness, which assumes or insinuates that subordinate and boss share common interests, see themselves as part of the same team and can operate on familiar, even familial terms, according to Morand.
Positive politeness is connoted by its friendly directness and the use of phonological slurring -- standardized ways of incompletely enunciating words or work phrases, such as "whassup" instead of "what's up."
People comfortable with positive politeness would use it even when broaching more sensitive subjects such as a raise or a complaint. However, positive politeness can often be construed as too forward or presumptuous, Morand said.
"One caveat should be pointed out," Morand added. "While politeness is a good attribute, excessive politeness, especially negative politeness, can make a person appear servile and can also interfere with clarity of communication in the workplace."