PRISM - American Society for Engineering Education - Logo - DECEMBER 2004 - VOLUME 14, NUMBER 4
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Model Behavior - By Pierre Home-Douglas - Photographs by Daniel Dubois

By Pierre Home-Douglas

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. 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.  - Photographs by Daniel DuboisHe 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."

Pierre Home-Douglas is a freelance writer based in Montreal.

 

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Model Behavior - By Pierre Home-Douglas
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