Nutty ideas spark Clark grain trust

In a physics laboratory in the Sackler Science Building at Clark University, researchers delve into questions such as why Brazil nuts are found at the top of a can of mixed nuts, what causes a snow avalanche and what holds a sandcastle together.

“You can get a Ph.D. in physics playing in a sandbox,” said graduate student Kevin T. Safford, standing by a giant tub of sand in the laboratory.

A $327,000 grant to Clark announced this week by the National Science Foundation will fund research on granular physics, the study of how masses of particles such as sand and grains behave. Arshad A. Kudrolli, an associate physics professor at Clark, will lead undergraduate and graduate researchers in a project: “Statistical and Dynamical Properties of Spherical and Non-Spherical Granular Materials.”

Mr. Kudrolli described his research as “trying to find out a few variables which capture the properties of granular materials.” The behavior of these materials must be studied

before developing mathematical formulas and physical laws to describe them, he said.

In a back room of the physics lab, a chain of metal beads vibrated slightly on an electromagnetic shaker, a vibrating plate, while a high-speed camera recorded its movement. Mr. Safford, one of the researchers working with Mr. Kudrolli, watched a movie of the chain’s movement on a nearby computer screen.

Mr. Safford analyzes numerical data generated from these movies to determine whether simple chains of metal beads can be used to model polymers, long complex chains of repeated molecules. The movement of a beaded chain might eventually be used to model the splitting of DNA in a cell or the behavior of E. coli bacteria, Mr. Safford said.

“It is applicable everywhere. I now have an opportunity to learn about all kinds of things that I’ve never studied before,” Mr. Safford said.

The grant will allow the lab to purchase a more advanced high-speed camera and more computers. This new technology will accelerate the experimentation process, allowing the researchers to do more, Mr. Safford said.

Researchers in the lab have studied why Brazil nuts usually end up near the top of a can of mixed nuts, a counterintuitive phenomenon since Brazil nuts are the biggest nuts in the mix. According to the Brazil nut effect, Mr. Safford explained, larger grains will often remain at the top of a granular mix because smaller grains can fall through the spaces to the bottom.

Ashish V. Orpe, a post-doctorate researcher in the lab, said masses of grains behave like solids when they are in a heap, like liquids when they take the shape of a container, and like gases when they are shaken. He said the kinetic theory of gases can be applied to agitated grains.

“It shows all three stages of matter within a single system,” Mr. Orpe said.

Mr. Safford pointed to a newspaper article hanging on the lab wall about the collapse of an earth wall on a parkway in Los Angeles. The researchers hope to eventually prevent these types of catastrophes by modeling granular properties.

Mr. Kudrolli left for Europe Tuesday, to be a visiting professor at the University of Liege in Belgium and attend a granular and granular-fluid flow workshop organized by the Gordon Research Conference in Oxford, England, at the end of this month.

His work has been featured in New Scientist Magazine, Nature Physics, National Geographic and Popular Science magazine and on CNN. He has been at Clark since 1997 and is a visiting scholar at MIT.

“Professor Kudrolli has been studying the behavior of granular media with support of the NSF since he arrived at Clark and has become one of the young leaders in this field,” Christopher P. Landee, chairman of Clark’s physics department, said in a press release.