Sediments in marshy water are instructive, she explains, because they contain pollen, seeds, diatom skeletons, and other traces of their time. These reveal the plant and animal life, and thus the climate. The sediments "just lay down very slowly and quietly," forming layers almost as clear as tree rings. So today, looking at sediments from places like Dan's Bog, Maryland, Brush can understand the climatic and ecological shifts of the past 12,000 years.
The sediments speak especially clearly for the last 350 years, because since the original forest was put to the plough, much more sediment has run off into the water. By the late 1800s, Maryland was only 20 percent forested. Brush says "you can correlate the amount of organic carbon directly with human development in the drainage area." Once, it took the mother of all hurricanes to lay down a centimeter of sediment, more than 1,500 years to lay down 10 centimeters. Today, a centimeter may deposit in one routine year.
Brush says the most fundamental change has to do with the character of the Bay itself, which used to support predominantly bottom-dwellers--such as oysters, flounders, sheepshead, and burrowing organisms. They lived on a firm bottom, protected by seaweed and many long aquatic grasses. "The water must have been very clear," she says.
Today, the Bay's bottom is silty, and throngs of surface-dwelling plankton keep light from the bottom and use up much of the water's oxygen. "So there's not very much life on the bottom any more," says Brush. Little but plankton and surface-dwellers like bluefish now lives in the Bay.
Plankton are nourished by nitrogen and phosphorus, and therefore the major cause of their rampant growth is pollution--but it's not all from sewage, she emphasizes. "Sewage has a local effect. It's very available to plankton because it's fluid, so it isn't transported very far, and you could ideally sacrifice one area for the cause of sewage." Rather, the major problem is "non-point" pollution, that is, pollution that comes in not from a single point (like sewage), but from so many places it's impossible to track down and control.
Primarily that means fertilizers, both from lawns and farms. These are particles, Brush points out. Therefore the water spreads them a long, long way before they degrade enough that plankton can chow down on their nitrogen and phosphorus. "The effect is just universal."
The sediment cores do reveal some tiny improvements in recent years, especially where the source of pollution was a point source, either sewage or industrial. "Sedimentation definitely decreased in the 1930s," Brush says, "from farm abandonment and soil conservation." She also sees siltation improving in some areas since the '70s. However, the 1970s also saw a dramatic loss of submerged aquatic grasses. "That was immediate, widespread, and had never occurred before," Brush notes.
The natural cycle, of course, is one of change also. Seven thousand years ago, the dominant tree of the coastal plain was hemlock, which prospers where life is wet. (Today, Maryland hemlock grow only in the mountains.) Only 5,000 years ago did oak begin to take over, showing that the climate had gotten dryer. Sedimentation from that period also shows a lot of fires (revealed by carbon), and the concomitant blueberries and other undergrowth that need open land. Then, 1,000 to 1,200 years ago, the area went through the so-called "medieval warm period," a couple of centuries of drought, heat, and scant vegetation. In Greenland at that time, the Vikings grew wheat.
The Bay and the land around it can adapt to these natural changes, says Brush. "The organisms have evolved in a very dynamic, cyclic estuary--storms, climate shifts--even after big hurricanes things recover very quickly." What the biota of the Bay are not adapted to, she says, "is the kind of continuous change imposed by people," century after century. --EH
The top quark is one of the 12 subatomic particles thought to make up all of matter, according to the Standard Model of physics. If its existence is confirmed, it clinches the Model.
The latest evidence comes from an atom-smashing experiment at the Fermi National Accelerator Laboratory outside Chicago. In the experiment, protons and their counterparts, anti-protons, are smashed together at super- high speeds. The collisions produce a variety of subatomic particles including top quarks, which last for only a fraction of a second before decaying. Physicists hoped to confirm that top quarks had been produced by looking for evidence of their decay products: bottom quarks and w particles. Now, in the recent experiment, an instrument called the Silicon Vertex Detector noted the presence of bottom quarks. Barnett was one of a dozen scientists who originally designed the instrument.
For the recent finding, physicists analyzed data from a trillion proton-anti-proton collisions collected at Fermi during 1992 and 1993. Twelve of the trillion appear to have each produced an "event," says Barnett, meaning an interaction yielding a top quark. "It's pretty strong evidence for a top quark," he says, though more events in the ongoing experiment will probably be necessary to say so with complete certainty. "How many hairs does it take to make a beard?" asks Barnett. "One is not enough. Two isn't. But is 100? Just when evidence [finally] becomes a discovery is sort of arbitrary." --MH
The further along of the two projects, the Applied Physics Labor- atory's Flare Genesis solar observatory (top), is scheduled for launch from the South Pole in December. The observatory--a 32-inch aperture optical telescope carried by a free-flying balloon filled with 28 million cubic feet of helium--is the most powerful solar telescope ever flown. It will help astronomers understand how solar flares arise, says APL solar physicist David Rust.
Solar flares are explosions of charged particles on the sun's surface, observed in a cycle thought to peak every five years. They distort the Earth's magnetic field, which disrupts communications systems and electrical power. "We think solar flares have to do with currents and the sudden catastrophic collapse of magnetic fields," says Rust. But viewed from Earth, details of the magnetic structures are blurred by the Earth's atmosphere. Flare Genesis, riding 125,000 feet up--above 99 percent of the atmosphere--will have a clearer view, says Rust.
In a separate project, astronomers Holland Ford, of Hopkins and the Space Telescope Science Institute (STScI), and Pierre Bely, of the European Space Agency and STScI, recently announced a proposal for a balloon-borne Next Generation Space Telescope.
The telescope will be slung below a helium-filled balloon larger than a 747 jet (something like the one below). "It looks a bit like a pregnant guppy," says Ford. Tethered to a mooring station, the telescope will ride 40,000 feet above the Earth, providing a "space-like environment," he says, at a cost of less than $100 million.
The telescope will have segmented mirrors that together will have 2.5 times the resolution of the Hubble Space Telescope. Though it will not observe ultraviolet light as well as Hubble does, it will see extremely well in the infra- red range of the spectrum--something Hubble cannot do. --MH
The analogs, unfortunately, are difficult to synthesize. But that task may get easier now that Posner has identified a key mechanism that gives artemisinin analogs their lethal punch against Plasmodium.
From their previous studies, Posner and his colleagues knew that the active component in artemisinin is a six-atom ring called a trioxane, which contains three oxygen atoms and three carbon atoms. Their theory goes like this: Injected intramuscularly into animals, the trioxane-containing compound zeros in on those red blood cells containing Plasmodia, because the parasites are unusually rich in iron. The iron triggers a cascade of chemical events in the trioxane, beginning with the transfer of an electron from the iron to the trioxane. That in turn triggers the formation of an oxygen radical, which plucks a hydrogen atom from a nearby carbon atom, transforming the carbon atom into what is called a "carbon centered radical."
These radicals are "known to be bad actors," says Posner. "They are known to disrupt DNA and to modify proteins, so it seems likely that this is what kills the malaria parasite." If so, the transfer of hydrogen, which Posner calls "hydrogen jumping," would be key to the whole cascade.
To test their theory, Posner's group hobbled the ability of several artem- isinin analogs to undergo hydrogen jumping, then tested the drugs' ability to destroy Plasmodia-infected cells. The team then tested a control group of analogs: drugs that had been chemically altered in a similar way, yet were still able to undergo hydrogen jumping.
Comparison showed that the analogs that could undergo hydrogen jumping were at least 100 times more potent, report Posner, former Hopkins graduate student Chang Ho Oh, now an assistant professor of chemistry in Korea, and current graduate student Dasong Wang. Posner says that their findings, reported in the April Journal of Medicinal Chemistry, "established for the first time that the hydrogen jump is a critical step in the mechanism of action of artemisinin."
In Posner's current studies, he is trying to streamline the synthesis of artemisinin analogs. The process currently takes two to four weeks and involves six or seven steps, he says. "We'd like to reduce that to three to four steps." The trick is to learn which parts of the chemical's structure are essential--the hydrogen jumping capability, for example--and which are expendable. The recent finding, he says, "gives us a chance to design other analogs in a rational fashion." -- MH
Poush's research actually started during his senior year of high school, when, with the help of Hopkins geneticist Victor McKusick, he published a study on the condition.
After he enrolled at Hopkins in 1991, Poush approached McKusick with the idea of genetically mapping "the finger." McKusick and geneticist Claire Francomano, a specialist in skeletal conditions, gladly gave him direction, money, and lab space. "When you have a trait that is inherited in a straightforward manner, and somebody has the energy, interest, and motivation in mapping it, I am all for it," says McKusick. "You can learn a lot about normal biology and embryology by studying an anomaly."
When Poush couldn't convince enough members of his family to donate blood samples for DNA testing, he decided instead to map a very similar condition, proximal symphalangism, a lack of the second-to-last joint on the index finger or toe. During the 1960s, McKusick had documented a 1,300-person extended family in which 400 members exhibited the trait.
That family provided an opportunity for a study with enormous statistical certainty, says Poush.
He spent last summer telephoning directory assistance, mostly in Ohio and Virginia, to track down members of the family, and he has managed to obtain 75 samples of blood, both from people with the trait and without it. "I got a whole range of responses," says Poush. "One man said, 'I've been waiting for you to call!' The guy has the finger and his kids have it. He's glad science is interested."
Poush has isolated DNA from the blood samples and is in the midst of mapping the proximal symphalangism gene using a technique called restriction length polymorphism. He heads off to graduate school next fall, at which time he plans to hand the project over to researchers at the National Institutes of Health. --KO
Undergraduates in engineering design and graphics, a course taught by assistant professor of civil engineering Martin Ramirez, recently thought up problems experienced by the handicapped, including those described above, and proposed devices to overcome them. Researchers from Hopkins's Center for Technology and Education helped with the course.
Every year, students in the class team up to attack a social problem using technological means. "A social problem fits into real life," says Ramirez. "You can't just have a good idea. It's got to be valued by society." Too often, he says, engineering students learn theories and equations but do not understand how to apply that information to real engineering problems.
In this year's class, Stephen Newman '95, an electrical engineering major, and his teammates proposed a wristwatch that provides a hearing-impaired person "hearing through touch," by vibration. In their plan, a modified smoke alarm emits radio waves of a frequency that triggers a motor in the wristwatch. The watch then vibrates intensely enough to wake a sleeping person, and it flashes "F" for fire.
"We tried to make the design open to anything, very versatile," says Newman. The watch could be programmed to respond to several radio frequencies, each from a different household device, and to display a symbol for each one: "P" for a ringing phone, "D" for a ringing doorbell, "O" for an oven timer.
Other student proposals include easy-grasp utensils with sphere-shaped handles, as well as a remote device the size of a credit card that allows a wheelchair-bound person to control an ATM from up to five feet away.
Some inventions from past years of the course have patents pending, says Ramirez, but students are not required to pursue patents. "My role is not to make my students rich," he says. "It is to expose them to real world engineering and motivate them." Ramirez was recently awarded a National Science Foundation Young Investigator Award to explore ways of improving engineering design education. --MH
Written by Elise Hancock, Melissa Hendricks, and Kate O'Rourke '94.