How practice makes perfect
So how do you get to Carnegie Hall? According to the findings of a Hopkins biomedical engineer, practice, practice, practice is only part of the story.

In the August 8 Science, Reza Shadmehr reports that for several hours after a person first learns a new motor skill such as playing the violin or riding a bike, the brain is hard at work consolidating and storing the new memory.

"We tend to think that practicing a task is the most important aspect," says Shadmehr. But this "offline learning system," he says, appears to allow for the brain's short-term storage region to teach new motor skills to the long-term memory system.

When a movement is learned, the right frontal cortex (image at left) is activated. Within hours, the memory is stored in the cerebellum (right) and anterior cortical regions (center). Photo by Reza Shadmehr

Sarabun, an oceanographer, and Ondercin, a physical chemist, at the Johns Hopkins Applied Physics Laboratory (APL), are leading a team of scientists who are studying where groundwater goes when it seeps into tidal rivers and estuaries. Solvents and other chemical wastes can penetrate the soil and contaminate the groundwater, which potentially can then carry these contaminants into rivers and bays, say the researchers.

The team ultimately hopes to determine whether groundwater rapidly dilutes, or if chemicals it carries remain concentrated, thereby posing a bigger threat to the health of plant and animal life. But to do that, they first must establish that they can trace groundwater, by telling it apart from the freshwater it seeps into.

During a recent early morning field test, the team rolled their research craft into Lauderick Creek, adjacent to the U.S. Army's Aberdeen Proving Ground. The creek flows into the Bush River, a tributary of the northern Chesapeake Bay.

The operation is obviously low-budget. The electrodes are the best money can buy, but milkcrates serve as chairs and computer tables. The scientists boot up their computers. Jim Velky, an electrical engineer, turns on a centrifugal force pump, which sucks up water through the tubing hanging out the back of the boat at a rate of one liter per second.

Groundwater enters a creek such as the Lauderick either by diffusing slowly along the shoreline, or by entering through gravel lenses in the soil underlying the creek, says Sarabun. But beyond that, scientists do not know much more. "People have measured groundwater [in the soil], but we don't know how it acts once it reaches an estuary," he says.

In soil, groundwater has characteristic features such as a low pH and low level of chlorophyll. By using their electrodes (which are sensors), the researchers hypothesize that they can see and map distinct regions within tributaries that bear this distinct profile.

Water sucked up by the pump now begins to flow across the electrodes. The sensors detect and measure pH, temperature, conductivity, lead, uranium, and chlorophyll count--data that appear on the computer monitor.

Today's test and field tests done earlier in the summer appear to support the team's hypothesis. They show a plume of groundwater first hugging the shore, and then gradually fanning out into the larger body of water. The scientists plan to use a mass spectrometer based at APL to screen water samples collected during the tests for noxious organic molecules. Their presence would indicate that groundwater has brought along contaminants.

The researchers say they can adapt their instrumentation to solve a number of environmental problems. In October, they planned to take their craft to Michigan, to study a heavily industrialized stretch of the St. Clair River. --MH

The contraption was the remote-controlled robot named Jason, which has traveled on dozens of undersea expeditions where human divers cannot survive, including a trip to the mid-Atlantic in the summer of 1996 (See the September 1996 Magazine).

Hopkins mechanical engineer Louis Whitcomb, along with Dana Yoerger and Hanumant Singh, of the Woods Hole Oceanographic Institution, designed Jason's navigation and control system--the "brains" that enable the robot to sense and maneuver around its environment. With funding from the Office of Naval Research, during the past year, the engineers boosted Jason's technical prowess.

Until recently, the robot could only be steered manually, by a pilot using a joystick in a control room. (Jason is tethered to a surface ship by fiber-optic cables.) Even the best piloting is far from precise, notes Whitcomb, and Jason's path was like a "drunken sailor's."

The robot had another limitation. Pilots had to land it before commanding it to unfold its robotic arm. Whitcomb knew that would not do for the Mediterranean expedition. Landing a two-ton robot on a field of priceless ancient pottery would not put Jason in the good graces of archaeologists.

So Whitcomb and his fellow engineers affixed a bottom-lock Doppler sonar device to the robot's underside. The coffee-can-size instrument measures the distance to the ocean bottom and records Jason's Doppler shift, which tells how fast Jason is moving toward or away from an object. This information allows Jason's control system to keep the robot on a fixed path, or to extend its arm while hovering.

During the expedition, which was organized by Robert Ballard, president of the Institute for Exploration, a Navy nuclear research submarine scoured the bottom for wrecks. Whenever it spotted one, it signaled back to scientists aboard a surface research ship. Navigating from a control room on the mother ship, Whitcomb and his colleagues then steered the robot in for a closer look.

During the six-week expedition, barnacle-encrusted amphorae and other artifacts that were retrieved from the sea floor almost daily won the "oohs" and "aahs" of the archaeologists, but the highlight for Whitcomb was of a higher tech variety.

"The most exciting part of the trip was one morning at 2 a.m. when we took our hands off the controls," says Whitcomb. As he and his colleagues observed on a control room monitor, they saw that their 2,200-pound "drunken sailor" had sobered up. Under its own steering system, it sailed smoothly and perfectly over a pre-programmed course.

Using its new Doppler sonar and with other instruments including cameras and a side-scanning sonar, Jason meticulously photographed the site and recorded the topography for every two centimeters of ocean bottom. "The topographic map is more detailed than any previous map in deep ocean," says Whitcomb.

Jason's journeys are not over. Next year, the scientists plan to take the robot to a field of hydrothermal vents in the Gulf of California. --MH

Fluoride in space
Hopkins astrophysicist David Neufeld recently discovered enough fluoride molecules in an interstellar cloud to fill 10,000 trillion, trillion tubes of toothpaste.

Toothpaste manufacturers are not about to start mining the skies, however. The newly discovered fluoride is 20,000 light-years away, in an interstellar gas cloud called Sagittarius B2. It is also in the form of a gas, hydrogen fluoride, not the element fluorine, which is used in toothpaste.

The discovery, the first sighting of fluoride in the interstellar medium, or space between stars, now gives astronomers the opportunity to see how hydrogen fluoride is produced in the interstellar gas, and thereby understand what this unusual medium is like, says Neufeld. "All stars and everything we're made of, and all the fluoride and everything else in a tube of toothpaste was at one time this interstellar gas."

The gas is a sparse, frigid medium, he explains. Millions of years ago, a slightly denser pocket of this gas collapsed under the force of gravity to form the sun and a spinning disk of material that eventually became the planets. Some of the fluorine in the interstellar medium became incorporated into these solid bodies. Thus, today, fluorine is found in soil, plants, and other materials throughout the Earth. But other fluorine atoms reacted with hydrogen molecules in the interstellar gas, to form hydrogen fluoride.

Neufeld and colleagues at Cal Tech and the Max-Planck Institute for Radio Astronomy, in Bonn, hunted for fluoride using the European Space Agency's Infrared Space Observatory satellite. Before the satellite's launch two years ago, astronomers had no means of observing hydrogen fluoride. That's because it absorbs light at a wavelength of about one two-hundredth of an inch, within the far infrared range of the electromagnetic spectrum. Such observations are not possible from Earth because our planet's atmosphere absorbs radiation at this wavelength.

The astronomers report their finding in the October 20 Astrophysical Journal Letters. --MH

Written by Melissa Hendricks

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