
September 4, 2002
For more information on these science news and feature
story tips, please contact the public information
officer at the end of each item at (703) 2928070.
Editor: Amber Jones
Contents of this News Tip:
Model of Plane
Impact at WTC Provides Clues to Structural Issues
Abolhassan AstanehAsl, a
civil engineering professor at the University
of California, Berkeley, has constructed
a realistic computer simulation of the
World Trade Center North Tower being hit
by a jet airplane. Astaneh's model has
simulated the first few seconds of the
plane's impact and entry into the building,
and he is refining the model to include
damage to the plane, the building floors
and the internal core columns. The next
step will be to include the effect of
fire heating the damaged structure and
initiating its final collapse.
The simulation will help analyze the potential
effects that different structural designs,
such as more robust core walls or more
fireproofing, might have had and the implications
for the design of future buildings.
Shortly after Sept. 11, Astaneh, a structural
engineer, obtained a National Science
Foundation (NSF) quickresponse grant
to investigate the collapse of the World
Trade Center towers and surrounding buildings.
He examined portions of the steel structures
removed from the site for recycling, recording
damage caused by impact and intense heat.
To build the model, he combined these
reconnaissance data, details from the
original building plans for the towers,
photos of the disaster and a model representing
a Boeing 767, using software donated by
the MSC Software Corporation.
Astaneh's study is part of an ongoing national
effort to provide engineers and architects
with technologies to strengthen buildings,
bridges and other physical infrastructure
against disasters such as earthquakes,
fire and explosions.Astaneh's NSFsupported
research has included the study of flexible
connections for semirigid steel frames
in low and midrise buildings, a steel
cable mechanism to retrofit multistory
buildings to prevent progressive collapse
due to blast, and a composite shear wall
system combining reinforced concrete and
steel plates in a new configuration for
seismic and blast protection. [Amber
Jones] 

Simulating the airplane's impact on the
building structure and the ensuing fire.
Images courtesy: Abolhassan AstanehAsl,
Univ. of Calif., Berkeley

Top of Page
Oceanographers
Probe Breaking Wave Bubbles, Ocean Processes with
New "Bubblecam"
The relaxing atmosphere of a walk along the shore,
especially the sounds of waves breaking on the beach,
continually lures people to coastlines.
For Grant Deane and Dale Stokes, oceanographers at
Scripps Institution of Oceanography at the University
of California, San Diego, the sounds of hundreds of
millions of air bubbles bursting at the shoreline
represent a key to understanding ocean phenomena.
The researchers, funded by NSF, used acoustical and
optical observations to determine that bubbles created
in breaking ocean waves play an important role in
a variety of ocean and atmospheric processes, including
airsea gas transfer, heat and moisture exchange,
aerosol production and climate change.
"Bubbles turn out to be the centerpiece for a range
of oceanbased and culturally important phenomena,"
said Deane. "They play a part in global climate change
because the global rates of carbon dioxide exchange
are in part dictated by bubblemediated gas transport."
The researchers developed a unique, hightech instrument
called "BubbleCam" to meticulously track the spectrum
of bubble sizes, the most important property of breaking
wave bubbles.
"BubbleCam is a highspeed video camera with an intricate
lens and lightfocusing system that lets us take finely
sliced pictures as waves break," said Stokes. "We
can gather all those images and feed them into a computer
that does the bubblecounting for us."
The results will be incorporated into models of bubblemediated,
airsea gas transport to help improve the models'
accuracy. The research may lead to the development
of new instruments that will allow scientists to remotely
monitor greenhouse gas transfer. [Cheryl Dybas]
Top of Page
What Makes
a Perfect Graph? Students of Math Get an Answer
What makes a perfect graph? The number of colors and
cliques, according to a group of NSF grantees which
has solved this 40yearold mathematical problem.
The researchersNeil Robertson of Ohio State University,
Paul Seymour and Maria Chudnovsky of Princeton University
and Robin Thomas of the Georgia Institute of Technologyreport
they have proved the Strong Perfect Graph Conjecture
after three years of study.
French mathematician Claude Berge proposed the conjecture
in 1960, describing the conditions that he believed
would characterize a perfect graph. Berge died on
June 30, 2002, just after the team proved his predictions
to be correct.
A graph is a collection of points of data and the lines
that connect them. A graph can illustrate, for example,
a network of radio transmitters or cellular phone
towers (points), connected by lines wherever their
transmission ranges overlap. The points can be colored
to illustrate frequencies.
The conjecture concerns the smallest number of colors
needed to allow the two endpoints of each connecting
line in the graph to be different colors. This number
is called the chromatic number, or chi, of the graph.
A clique is any group of points within the graph that
are all connected to one another. The minimum number
of colors, or chi, of a graph is at least as large
as the number of points in its largest clique. According
to the conjecture, a graph is perfect if, for the
graph and any subgraph created by deleting some of
the points, the chi equals the number of points in
the largest clique.
An example of a perfect graph can be visualized as
an efficient data transmission network. Thus, a phone
network based on a perfect graph would run most efficiently
with the minimum number of frequencies or channels
(colors) assigned to its transmitters (points) and
would continue to operate efficiently even if some
of the transmitters were knocked out. [Amber
Jones]
Top of Page
NSFNIH Grants
Will Integrate Mathematics and Biology
NSF and the National Institute of General Medical Sciences,
National Institutes of Health, have announced about
$24 million in funding over five years to encourage
the use of quantitative methods and computational
tools in biological research.
The 20 funded projects include statistical approaches
to DNA sequencing and genomics; the modeling of microorganisms,
pathogens, and acute inflammation; and studies involving
proteins.
Traditionally, federal support for the mathematical
sciences has come primarily from NSF. The new program
provides an additional source of funding for mathematicians
and encourages crossdiscipline approaches. The partnership
gives the medical sciences institute, which supports
research and training in the basic biomedical sciences,
access to a broader pool of math researchers.
Other areas of collaboration between NSF and NIH include
training in bioengineering and bioinformatics and
a cooperative biodiversity program. [Amber
Jones]
For the list of grants, see: www.nigms.nih.gov/news/releases/biomath.html

