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Humboldt Field Research Institute

Posted May 20, 1999

Search for Patterns Intrigues Physics Student

Anybody who sews, works with wood or enjoys a walk along a beach knows patterns. Repetitive shapes and forms are everywhere, and understanding them has been a driving force for scientists for centuries. For physicist Marty Ytreberg of Argyle, a Ph.D. candidate in the University of Maine Department of Physics and Astronomy, the search for explanations of patterns has led to magnetic fields and an unusual liquid.

Ytreberg conducts his research in collaboration with Susan McKay, chair of the department. He received his Bachelor’s degree from Walla Walla College in southeastern Washington and came to UMaine because of its rural setting and diverse physics faculty. His labors produced a significant milestone in March with publication of his first paper in Physical Review E. He also gave a presentation on his research to the Centennial Meeting of the American Physical Society in Atlanta.

Ytreberg works with ferrofluids, substances that are a hot topic in the world of high quality audio speakers. Ferrofluids consist of tiny magnetic particles, such as magnetite, a magnetized form iron-oxide, suspended in a fluid. Oil, kerosene or water will do. The particles are coated with a substance that keeps them from clumping together, and unlike beans in a pot of soup, they never sink to the bottom at room temperature.

These fluids perform their tricks, Ytreberg explains, when they are placed in a magnetic field. "What happens to them is that the particles will start to chain together. If you sit around and wait, say for an hour, you find that these chains clump together and form columns. The columns are all approximately equal in size. They’re approximately ellipsoidal or cylindrical in shape, and they’re about equally spaced from each other," Ytreberg says. In one word, patterns.

"If you look at the top surface, since the columns are about the same size and equally spaced, you see a hexagonal pattern. But if you increase the magnetic field beyond a certain amount, you can begin to see labyrinth patterns," he says.

What Ytreberg wants to do is to predict what the pattern will look like under any particular magnetic field or with a given volume and shape of ferrofluid. Although the fluids have practical applications in speakers, some types of machinery and even medicine, Ytreberg’s studies fall squarely into the realm of basic science. Such studies can have enormous practical benefits, but they are based in curiosity for its own sake.

In Ytreberg’s case, the road for his curious adventure is mathematics. With pencil and paper, he works with groups of equations and solves them in order to develop a precise picture of what happens to the ferrofluid. Since the process can get extremely complex, he makes a variety of assumptions to simplify things a bit. In a sense he takes short cuts. By experiment, he explores the mathematical consequences of one assumption after another. The data for his studies come from published reports.

The fuel for these studies is strictly brain power. Although Ytreberg uses a computer to check his calculations, he isn’t doing computer simulation which, he says, would not be useful for his particular approach to the problem. Moreover, simulations can be misleading. "One of my favorite quotes is that the problem with computer simulations is that they always give you a result. So you always get something out of the simulation, and you’re usually too eager to accept that as true," he says.

In addition to the ferrofluid studies, Ytreberg has also worked with a related area known as reaction-diffusion equations. Solving these complex equations yields more patterns. In fact, some of these patterns are similar to those that have been observed in ferrofluids. No one has yet been able to explain why these similarities exist.

Ytreberg admits that he may not reach his goal but considers his work to be excellent preparation for investigating current topics in physics. "Non-linear physics or non-linear dynamics is a rapidly growing field. Both of these systems I’m working with are highly non-linear. I think I’m preparing myself well for a broad field survey on non-linear physics or condensed matter physics."

Eventually, Ytreberg would like to work in a university as a physics teacher and researcher.

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