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January 29, 2001

For more information on these science news and feature story tips, please contact the public information officer at the end of each item at (703) 292-8070. Editor: Tom Garritano

How Cold is Cold? Scientists Now Know For Sure

Thirty-five years ago, a University of Florida physics professor suggested a new way to measure very low temperatures -- that is, temperatures so cold they were off the official scale, which at that time stopped at 0.65 Kelvin.

E. Dwight Adams and graduate student Richard Scribner, with support from the National Science Foundation (NSF), created a new type of thermometry by determining the pressure and temperature needed to freeze helium-3. As more and more research was performed in exteme cold, scientists used this method to gauge temperatures that sometimes approached 0 degree, the theoretical absolute zero.

Now, the International Commission on Weights and Measures has officially adopted Adams' "melting pressure thermometry" gauge as the worldwide standard for measuring the ultra-cold.

Adams' NSF-funded research in magnetism and ultra-low temperatures spans more than three decades, dating to his invention, with graduate student Gerald Straty, of the pressure gauge that allowed the measurements to be made. He now serves as director of a user facility at the NSF National High Magnetic Field Laboratory at the University of Florida, the nation's premier facility for research into magnetism. [Amber Jones]

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New Model Provides Reasons For Climate Change Observations

A new research model uses biological factors to quantify the processes behind ecological responses to climate change. The work at Penn State University, funded by NSF, is moving beyond previous observational limits and providing a way to analyze factors that can accelerate spring events, said Penn State researcher Eric Post.

Using data for three species of flowering plants collected during a 50-year period, Post and his collaborators applied a mathematical and statistical approach developed originally for studies of population dynamics. The model incorporates variables such as competition for resources and population density, which are factors likely to change with climate, according to Post.

In each of the three species - wood anemone, hepatica and colt's foot - the model shows that plants bloomed earlier after warmer winters because of complex interactions involving competition, climate and resources.

"We hear with increasing frequency reports about birds nesting earlier and flowers blooming earlier," said Post. "Those reports get a lot of attention because they provide convincing evidence that species are responding to climate change. But if we really want to understand what's happening and make predictions about what will happen with future climate changes, we need to get at the mechanisms and relationships behind the changes." [Cheryl Dybas]

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Glitches in Earth's Wobble Help Geophysicists Probe Planet's Core

Millimeter deviations from the expected wobble of the Earth's axis are giving geophysicists clues to what happens 1,800 miles underground, at the boundary between Earth's mantle and its iron core. The research is funded by NSF.

The new theory proposes that iron-rich sediments are floating to the top of Earth's core and sticking like gum to the bottom of the mantle, creating drag that throws Earth's wobble off by a millimeter or two over a period of about 18.6 years.

"The wobble is explained by metal patches attached to the core-mantle boundary," says Raymond Jeanloz, a geologist at the University of California at Berkeley, who conducted the research with colleagues Bruce Buffett of the University of British Columbia and Edward Garnero of Arizona State University. "As the outer core turns, its magnetic field lines are deflected by the patches and the core fluid gets slowed down."

Now, with 20 years of data, says Jeanloz, "we can confirm that the discrepancy is there and is explained very nicely by the Earth's magnetic field causing friction at the bottom of the mantle." [Cheryl Dybas]

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