Icy adventures. Camping out in a small yellow canvas tent in subzero weather may not be to everyone's taste, but for Adam Lewis that tent has been home during the three months of the Antarctic summer for the past several years. Lewis (GRS'03), a doctoral student working with College of Arts and Sciences Earth Sciences Assistant Professor David Marchant, recently won the Provost's Award at BU's Science Day 2001 for his studies of ancient glacier ice in Beacon Valley, Antarctica.
Lewis' research focuses on the age and origin of this ice, discovered by Marchant in 1995. Marchant theorized that it was a relic of an ancient ice sheet and established its age at more than 8.1 million years by dating volcanic deposits lying above the ice. This conclusion was immediately controversial. Others claimed that the ice could have formed in place from ongoing freeze-thaw processes or that it could be the far younger remains of local glaciers.
To test these theories, Lewis and fellow graduate student Eric Moore (GRS'01) systematically collected samples of buried ice and of covering sediment, called till. Laboratory analysis revealed identical physical characteristics in the two sample sets, including rock fragments found only in mountains far from Beacon Valley, providing strong evidence that both came from the same source outside the valley.
Lewis also used a novel approach, measurement of a cosmogenic isotope of helium (3He), to confirm the long-term stability of the ice. This rare isotope is created when cosmic rays from deep space collide with molecules at the Earth's surface. The 3He collects within mineral crystals in rocks, and the amount detected indicates how long a rock has been on the surface. As you move deeper into the Earth, the concentration of 3He decreases. Lewis found that the till above the glacial ice showed a systematic decrease in 3He with depth, indicating the soil covering the ice had been stable for millions of years, but the drop-off was quicker than expected. This result would be explained by slowly sublimating (evaporating) ice, and a resulting compaction of the till above. The 3He levels were used to calculate the sublimation rate of the ice, a calculation that confirmed the ice could have survived more than 8.1 million years.
This year Lewis came home from Antarctica with another, possibly even more interesting, result. Close examination of till and ice samples reveals the presence of organic matter -- simple animal and plant remains such as nematodes and diatoms -- that may prove to be some of the last plants and animals to inhabit the interior of Antarctica before the massive East Antarctic Ice Sheet extinguished all life there more than 10 million years ago.
Lighting the way. Engineering doctoral student Matthew Emsley (ENG'03), winner of the H. J. Berman "Future of Light" Prize in Photonics at Science Day 2001, is developing a new technology that has the potential to dramatically reduce the cost of photoreceivers in optical networking and may lay the basis for new developments in medical imaging.
Typically an optical network transforms digital information to light via a laser that generates a series of signals on a particular wavelength. The signal is sent along a fiber-optic cable to another computer, where a detector takes the optical signal and transmits it to a chip that translates the information back into digital information that can be read by the computer. Current detectors are generally made of gallium arsinide (GaAs), an expensive material, whose use has possible environmental concerns.
The technology being developed by Emsley, the silicon resonant cavity enhanced (RCE) photodetector, is made entirely of silicon, a less expensive alternative than GaAs. The new detector is also more reliable since it can be totally integrated with the associated silicon chip with embedded electronic circuitry to produce a single integrated device rather than a series of connected parts. The detector builds on the RCE photodetector, developed by Emsley's advisor, College of Engineering Associate Professor of Electrical and Computer Engineering Selim Unlu. It uses a unique arrangement of mirrored surfaces separated by a cavity that reflects and amplifies the incoming optical signal. This ability is vital since silicon does not normally absorb light efficiently.
Unlu and Emsley have applied for a patent on the device, and are currently working on building arrays of the detectors for applications in medical imaging.
Briefs" is written by Joan Schwartz in the Office of the Provost. To read
more about BU research, visit http://www.bu.edu/research.