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Transition Fan

Professor of Physics Jan Tobochnik is a self-described “big fan” of phase transitions–solids to liquids; liquids to gas; magnetic to non-magnetic; the fall of the Soviet Union. Just a few examples of spectacular phase transitions, and phase transitions are “always interesting,” says Tobochnik. Also, some systems act like they are at a phase transition, such as perhaps the neural firings of the brain. In particular, he’s intrigued by the physics associated with the very moment of change–a period of “criticality” at which all scales of behavior are important.

So it’s no surprise that for the next three years his research (supported by a grant from the Petroleum Research Fund) will involve reproducing experimental data and generation of new data through computer models of melting. Wait…melting? Surely a phenomenon as long observed as this (just set an ice cube on the counter) is thoroughly known to science. Not so, says Tobochnik. “Science has no comprehensive theory for three-dimensional melting,” he says. “Consider that ice cube on the counter–we know it melts from the outside in, but we only know the mechanisms for melting related to surfaces or defects. Absent a surface or a defect, we don’t know how a material melts. We have no general theory, which, in the case of new materials, makes the prediction of melting points and other properties unreliable.”

Two very recent–and painstaking–experiments (one at Harvard, the other in China) managed to explore the phenomenon of melting when there are no surfaces or defects by using colloidal spheres suspended in a fluid. The result was some fascinating new data. But the experiment is extremely difficult to set up, making replication, confirmation, and extension of the data a problem. Tobochnik’s grant will enable his lab to work with the Harvard group to set up a computer modeling simulation of the experiment. That modeling will confirm and, hopefully, provide new knowledge of melting in three dimensional substances.

The grant will fund two students in Tobochnik’s lab for three consecutive summers. They may, or MAY NOT, be physics majors doing SIP work. “Many times I prefer to provide significant research experiences to younger students, including first-years,” Tobochnik says.

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