Tiny bubbles. What could be more calming than watching snowflakes drift serenely onto a smooth surface of water?

If you are an animal that lives in that water, however, landing snowflakes create an enormous racket due to bursting air bubbles, according to a preliminary study by ENG Associate Professor Ronald Roy and colleagues from the University of Washington, University of Edinburgh, and Johns Hopkins.

Snowflakes are ice crystals that have one-tenth the density of water, which means they are about 90 percent air. When a snowflake strikes water, it melts, freeing up that air mass, which oscillates and makes noise.

By analyzing recordings made underwater during winter storms, Roy, a specialist in aerospace and mechanical engineering, and his fellow researchers found that when a snowflake lands, it deposits a tiny amount of air just below the water's surface, creating a bubble. Just before this air bubble reaches the surface and pops, its surface volume adjusts and oscillates, which sends out a high-pitched noise.

This sound ranges from 50 to 200 kilohertz, too high-pitched for human ears, which generally don't hear anything above 20 kilohertz. But, according to team members, the aggregate snowflake-produced noise could add 30 decibels -- a three hundred-fold increase to underwater noise levels, which annoys porpoises and other aquatic animals that can easily detect these higher frequencies.

In addition to its impact on water animals, snowflake noise can create problems for sonar devices that track migrating fish or instruments that are designed to distinguish between natural and human-made sounds. The team's findings might help engineers develop equipment that can filter out the sounds of falling snowflakes, and so they intend to continue to study the dynamics of bubble oscillation and air encapsulation to determine exactly how the sound is produced. The research appeared in the October 1999 Journal of the Acoustical Society of America.

Small loss is a big gain. A new study by MED Assistant Professor of Medicine Lynn Moore (MED) shows that overweight people who lose as little as one pound a year can significantly lower their risk of high blood pressure.

Using data from the landmark Framingham Heart Study, Moore looked at about 400 study participants between the ages of 30 and 65 who had lost four or more pounds during the first four years of the study -- which began in 1948 -- and kept it off for four more years.

Participants between the ages of 30 and 50 who lost the weight were about 25 percent less likely to develop high blood pressure over the next 40 years than men and women who stayed the same weight. People between the ages of 50 and 65 lowered their risk by 30 percent.Those who lost the weight and then regained it had no benefits, but were not harmed by the gain.

"It's amazing, isn't it?" Moore told the Associated Press. "Even that modest amount of weight loss makes a big difference. That's an exciting public health message."

The medical community has long known that excess weight is an important cause of high blood pressure. High blood pressure forces the heart to work harder and thus plays a significant role in strokes, heart attacks, and other diseases.

Moore presented her findings at the March 3 meeting of the American Heart Association.

"Research Briefs" is written by Janice Zazinski in the Office of Public Relations. To read more about BU research, visit http://www.bu.edu/research.