ENGINEER SPOTLIGHT: Peter Cummings - Model Behavior
A LEADING EXPERT IN COMPUTER
MODELING AND MOLECULAR SIMULATION, VANDERBILT PROFESSOR
PETER CUMMINGS IS DEVELOPING ONE OF THE MOST ACCURATE
MODELS OF WATER EVER CREATED.
Trying to predict the way cancerous tumors will spread,
exploring the possibility of how life on Earth may have
begun at deep-sea vents, investigating ways to create
new materials one molecule at a time: Not your typical
idea of what chemical engineers do—especially
one chemical engineer. But then Peter Cummings is known
throughout his field as a quick study, adept at coming
up with novel ways to solve diverse problems using mathematical
modeling and computer simulation. He is also someone
who thrives on allying himself with people in different
fields whom he readily admits "know infinitely more
about a subject than I do." As Douglas LeVan, chair
of the chemical engineering department at Vanderbilt
University puts it, "Peter collaborates very well."
A lot of that versatility has to do with his background.
The John R. Hall Professor of Chemical Engineering at
Vanderbilt began his career thinking he'd end up in
physics. He recalls how at the end of his first year
of studying science in his native Australia, the head
of the mathematics department approached him and told
him his future should be in mathematics. "I was equally
successful in chemistry and physics," the 50-year-old
father of two recalls, "but the head of the chemistry
department never called me in to convince me to switch
to chemistry." Cummings says the fact that the mathematics
chair was an American was probably not coincidental.
"He had the type of aggressive mentality that other
department heads didn't have in Australia at that time.
Definitely an American thing—to headhunt me out
of another department."
Cummings completed his Ph.D. in applied mathematics
at the University of Melbourne in 1980 and then went
to the University of Guelph in Canada and SUNY Stony
Brook as a post-doc in physics and chemistry respectively.
When he started looking around for permanent work, colleagues
encouraged him to apply for posts in chemical engineering.
"Actually I had never published anything in a mathematical
journal as a Ph.D. student; it was all in chemistry
journals." Cummings says there was a significant shortage
of faculty in chemical engineering at the time. "They
were looking for new blood." One of the people who helped
guide him in his new career—a man he considers
a mentor—was Keith Gubbins, now professor of chemical
engineering at North Carolina State University. "He
had originally written to me when he was a graduate
student looking for a post-doc. I didn't have anything
for him at the time but we stayed in touch," Gubbins
says.
Gubbins urged the University of Virginia to invite
Cummings for an interview. They did and he got the job.
Gubbins says that Cummings is someone who made the transformation
from mathematics to chemical engineering relatively
seamlessly, but not everyone can. "It depends on the
personality and attitude of the individual. If they
are genuinely interested in finding different ways to
apply their background to chemical engineering problems
then they can make a huge contribution—as Peter
has."
Cummings worked for over 10 years at the University
of Virginia before taking a joint position as distinguished
scientist at Oak Ridge National Laboratory (ORNL) and
distinguished professor at the University of Tennessee.
In August 2002 Vanderbilt lured him to Nashville, partly
on the strength of the university's renowned medical
facility and Cummings's interest in biological research
and the fact that he could continue working at Oak Ridge.
To juggle the two posts, Cummings keeps an apartment
in Nashville as well as a home in Oak Ridge, near Knoxville,
where his wife works as a networks manager at the University
of Tennessee.
At Vanderbilt he soon linked up with Vito Quaranta,
professor of cancer biology, to investigate how cancerous
tumors spread. As Quaranta explains, predicting cancer
is a little like predicting the weather: You can't be
sure how it will develop. Another similarity: "You want
some numbers. Just like being able to say the chance
of rain tomorrow is 20 percent, you want to have some
idea of the chance that a cancer is going to spread."
"The reason predictions are not as accurate as they
should be," says Quaranta, "is because of the sheer
mass of information and the lack of adequate computer
power." Enter Peter Cummings with his mathematical modeling
to understand the wealth of data. Cummings employs the
technique that he uses in other areas of research: looking
at a level lower, where things are less complicated—in
this case, examining single cancer cells and then using
computers to look at their behavior to determine a so-called
"emergent collective behavior" that occurs when cells
combine to form a tumor.
PLAIN OLD WATER
Cummings's "one-level-down" technique has proven particularly
helpful in his attempts to understand water. He and
his group have worked for the past eight years on designing
the most accurate molecular model of water ever developed.
Water is ubiquitous and essential to life, but it is
far from simple. As Cummings points out, H2O displays
lots of anomalies, becoming less dense, for example,
as it freezes, unlike virtually all other liquids. Cummings
hopes that by creating the world's best model of the
water molecule, scientists and engineers around the
world will have better predictive power to know how
water will behave in different situations. One that
he has investigated is high-pressure, high temperature,
like the type of water found at the bottom of oceans
surrounding hot vents of water gushing up from the ocean
floor. It is here that scientists have discovered life
that survives not on light, which drives photosynthesis,
but a chemical synthesis based on hydrogen sulfide.
Theories have surfaced that life on Earth may have begun
in similar communities billions of years ago before
the ozone layer enveloped the Earth in its protective
cover.
The trouble is, as Cummings points out, it's almost
impossible to do experiments where the water is 600
degrees Celsius and the pressure is 400 times that at
sea level. "You or I wouldn't last a second here." Part
of his simulation has shown how organic modules, the
building blocks of life, are actually more soluble at
high pressure and temperatures, exactly the type of
environment that deep-sea vents provide. This information
could be useful for researchers trying to solve environmental
purifications problems by using more-efficient solvents.
Despite the fact that Cummings is an expert in water
and aqueous solutions, as well as editor of one of the
top journals of chemical thermodynamics, Fluid Phase
Equilibria, 90 percent of his funded work today centers
on the emerging field of nanotechnology. As someone
who has studied materials on the one-molecule or one-cell
scale, Cummings says that in nanotechnology he is applying
techniques that he has been using for the past 20 years.
"You lay three water molecules side by side and you
have a nanometer worth of water molecules," he explains.
"In a way we feel like telling the experimentalists
‘Come on down. Welcome to our domain. We've been
waiting for you.'"
Nanoscience also appeals to the collaborator in Cummings;
it is highly interdisciplinary. As well as teaching
at Vanderbilt, he serves as the director of the Nanomaterials
Theory Institute, part of ORNL's Center for Nanophase
Material Sciences. He frequently teams up with other
scientists and engineers from throughout North America
and Europe. Among his current activities is one as principal
investigator on a National Science Foundation-funded
research project on POSS cubes, nanostructures that
fellow researcher Sharon Glotzer from the University
of Michigan calls "silicon's answer to Bucky Balls."
The cubes are basically empty "cages" made from eight
silicon atoms at the corners and an oxygen atom along
each of the cube's 12 edges. In the simplest POSS molecule,
silicon also has a hydrogen atom attached, which can
be replaced chemically with many different kinds of
molecules to create hybrid materials with properties
nature itself could never produce, such as coatings
for spacecraft.
Cummings provides his knowledge in theory modeling
and simulation to figure out how these structures will
then work on a much larger scale. In nano work, computer
simulation proves particularly useful since experiments
are difficult to perform at the molecular level, even
with the advent of inventions like the tunneling electron
microscope.
Despite all his research, Cummings hasn't lost sight
of one of his responsibilities as a professor: Every
year he instructs a graduate class in the fall and an
undergraduate class in the spring in process control.
He has noticed a deterioration of math skills over his
20 years of teaching. "A lot of it is probably due to
the sheer range of tools students now have available,
including symbolic manipulation packages like Mathematica.
I'm not sure it's necessarily bad; they're stronger
in other areas, like doing complicated statistical analysis
and analyzing and presenting data." He recalls a colleague
who wrote an article on seeing how far people could
get in the theory of fluids only being able to use equations
written in the sand. "I figure if I were stuck on an
island with a very long beach I could get a lot farther
than these students. But," he adds with a laugh, "they're
not going to be stuck on an island anytime soon."
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