Johns Hopkins Magazine - June 1996 Issue

In Short - Science & Technology

By Elise Hancock and Melissa Hendricks
Humbel charcoal holds high-tech promise how infants use nouns "much columns" of magma holding stars together with dark matter

Turning wood into brakes and satellites

Start with just plain wood. Pyrolize (heat-treat) it in the absence of oxygen, so no flames occur. Admire.

This humble charcoal is the basis of a way to make inexpensive high-tech brakes for trucks or a 747; to make furnace heating elements; to recycle pressure-treated wood; and in general, to transform wood into space-age, feather-weight stuff with better compressive strength than the original wood.

"Or you could use it for art and furniture," says Dennis Nagle, assistant professor of materials science and engineering in the Whiting School of Engineering. He picks up a chunk of clear plastic and hands it over; it holds a pyrolized dollar bill, every detail preserved in subtle shades of black. Even the serial number can be read.

That's Nagle's point, or part of it. "We can take a very detailed structure and pyrolize it, and retain every detail." The new process was developed by (now) postdoctoral fellow Christopher Byrne, PhD '96, as his thesis work.

The initial step consists of controlled pyrolysis, at temperatures that melt most metals--up to 6,000F--in argon or nitrogen. As the wood converts into carbon, size shrinks by one-fifth, weight by four-fifths--but only in the first heating. "Once it's been carbonized, it doesn't change," says Nagle. The material is now brittle, but dimensionally stable. "That's important."

Next step: carve the carbon into precisely the size and conformation desired.

Last, the conversion: add ingredient X to the carbon and heat-treat once more (in some cases several times). The result can be, basically, any product based in carbon. If ingredient X is silicon, for instance, heat-treating produces a ceramic--useful for anything from coffee mugs to catalytic converters.

If X is phenolic resins, which are 50 percent carbon, the result will be a carbon/carbon composite--strong, tough, lightweight, and durable. It withstands heat and cold and will retain its shape and size.

One use for such a material would be carbon/carbon composite brakes, like those used in 747s. In that case, there's a fourth step: coat the product with silicon and reheat, to give it a silicon carbide surface. As a ceramic, the silicon carbide protects the brakes from burning (friction heats the plane's brakes to 1500C).

Nagle and Byrne's brakes should be cheaper to produce, at least by comparison with current materials--they take weeks to make, starting with high modulus graphite fibers laid together tenderly just so, to align the fibers. That's one reason why the material used in 747 brakes costs $15,000 a pound. But wood, as Nagle points out, is "already aligned. It grows with all the fibers the way you want them." Wood-made brakes should be affordable for truckers and other markets.

Such use of wood is new, believe it or not. Manufacturers have been using alignments of graphite fibers as the basis for materials for many years now, but had overlooked the fact that wood can be converted into graphite fibers. "I couldn't believe it," says Byrne. "It's so obvious, once you see it. I guess, in a high-tech world, we all tend to think high-tech."

The concept has many more applications, says Byrne. Carbon-based composites show up in Stealth bombers, high temperature tubing, cutting tools, sports equipment, soaring planes, satellites, boat hulls --a list that could go on and on. "We'll substitute wood for anything they'll pay us to do it for," says Byrne, only half-joking. "Though I can't say I can do everything with it. I haven't yet learned how to make diamond."

Beyond high-tech materials, consider an environmental application: recycling pressure-treated wood from countless decks and porches--wood that is green with oxides of arsenic, copper, and chrome. Those three are heavy metals and highly toxic. That's why you should never build with treated wood indoors. Nor should treated wood go into landfills, where its toxins will halt natural decay in the landfill, and eventually reach groundwater. But of course, people dump old deck boards all the time.

Nagle and Byrne propose that treated wood be pyrolized to increase its porosity, so it could then be leached of heavy metals. These could be recycled to treat more wood, while the pyrolized wood could be used to make new high-tech products.

Nagle hands over another sample, a glossy black chunk flaunting the whorls of bird's-eye maple. "Furniture?" he wonders. "I think it's beautiful." It is, and so unexpectedly light for its size that my hand jerked up as I took it.

"Think of all the colors in the Painted Desert," Nagle says. "The petrified trees--all those colors come from minerals. You could do that on purpose."

Into the minds of infants

Babies deserve more credit than they are given. While a mother will gleefully exclaim, "There's a kitty!" to elicit a smile from her 9-month-old, her baby is doing some serious calculations. The baby is figuring out that all forms of feline--be they large, small, or newborn; calico, Persian, or mixed breed--belong to the same category: kitty. That's a big job. But assistant professor of psychology Marie Balaban finds that even before babies can talk, they use words they hear spoken to organize the world into mental categories.

"The mind is set up to make links between these familiar words and what they mean," says Balaban. Without language, humans would still categorize things--it would just take longer. "That's why we say language facilitates categorization."

Balaban and psychology professor Sandra Waxman, of Northwestern University, studied 9-month-old babies in a series of experiments to test this theory.

In one experiment involving 44 babies, an assistant who had not been told the purpose of the study showed each baby five different teddy bears for 15 seconds each. For example, a baby was shown a bright red teddy, followed by an aqua bear, and so on. The assistant also asked the baby questions, in the slow, exaggerated manner adults use when speaking to infants. (To control for the fact that the 9-month-olds may already have begun to understand words like "bear," the experimenters did not use those words but instead said "ursine.")

When shown a bear toy, half the babies were asked, "See the ursine? Do you like the ursine?" The other half were asked similar questions that omitted the object's name: "See what I have? Do you like that?"

After viewing the series of toys, each baby was then simultaneously shown two new toys. One was a new bear and one was a kitty toy or other object from a "novel" category. The amount of time the baby spent looking at each of the two new toys was recorded by students who viewed a film of the experiment and who were naive to the hypothesis.

Just as older people do, babies like novelty. So if the babies recognized that the kitty belonged to a new category, they would look at the kitty longer than the bear.

The key question was, Would the babies who had been asked about "the ursine" spend more time looking at the kitty than would the babies who had not heard the word for the category? If they did, it would support the theory that nouns guide babies in forming categories.

The researchers found that, in fact, babies who had been asked questions that included "ursine" (or "orca," "pinto," or "feline" in subsequent trials) looked at the animal from the new category for 62 percent of the trial period. In contrast, babies who had not heard the word "ursine" looked at each of the two new toys virtually the same amount of time. Balaban discussed her findings in April at the International Conference on Infant Studies, in Providence, Rhode Island.

Though the time differences are not dramatic, says Balaban, they are reliable and consistent in this and several other studies.

Dark and blue

Here's a strange beast: a spiral galaxy loaded with dark matter. In fact, the dark matter in the center of NGC2915 is 10 times denser than that found in other spiral galaxies, reports Hopkins astronomy postdoctoral fellow Gerhardt Meurer. But unlike the star-studded spiral arms of our own Milky Way, NGC2915 contains relatively few stars, all of which are located in its core (the central white region). The spiral disk of the galaxy (in blue) is neutral hydrogen gas, or gas that has not been ionized as a result of star formation. NGC2915 may be a galaxy whose attempts at star formation have failed except at its center.

Meurer, along with an international team of astronomers, recently discovered the strange properties of the galaxy through the Australia Telescope Compact Array, a series of radio telescopes in Narrabri, Australia. NGC2915, which is 17 million light-years away, is a blue compact dwarf galaxy, so called because it is relatively small compared to elliptical galaxies or other spiral galaxies, and because the stars at its core are hotter (therefore, blue).

With its trove of dark matter, NGC2915 may help astronomers better understand the nature and role of this invisible stuff, which is thought to account for the majority of matter in the universe. "No one really knows what dark matter is," says Meurer. Being invisible, it is also difficult to detect, and astronomers infer its existence through its gravitational tug. For Meurer's purposes, he found that he could use NGC2915's neutral hydrogen to determine the amount of dark matter present.

The dark matter in NGC2915, says Meurer, might act like "glue" that aids star formation. "Not a 'glue' in the sense of being sticky," says Meurer, but in the sense of tugging with an immense gravitational force. "You need to have something that holds stars together, or they get blown apart by all the energy of events like supernovas, or the death of stars." In normal galaxies, stars and gas provide this gravitational force. In NGC2915, dark matter appears to do the job.

A new take on how Earth's crust is formed

Bruce Marsh slides open tray after tray of the cabinets that line the halls of Olin Hall, revealing ebony basaltic rocks, grainy granite stones, and hunks of limestone. "The Earth has a greater variety of rocks than any other planet in the solar system," exclaims Marsh excitedly. Admittedly, not everyone gets as excited about granite and basalt as does Marsh, a professor of earth and planetary sciences. But where others see just stone, Marsh sees historical records that can explain how the continents were formed.

And he's come to conclude that the conventional theory about how the continental crust is generated is flawed. Based largely on research conducted during three expeditions to Antarctica, he has completely rewritten that theory.

One part of the conventional theory remains undisputed, which is that the continents were formed by magma surging up from deep within the Earth and pushing apart masses of land. The process continues today, as pieces of continental crust are continuously detaching, then being remelted and recycled. Within the magma, crystals of various sizes and chemical composition are born, and certain highly distilled material eventually becomes continental crust.

But traditional beliefs about how crystals are formed and how magma flows are wrong, says Marsh. According to the conventional view, magma is injected, from deep within Earth's mantle, into large subterranean vats called magma chambers. "But nobody was clear on what these magma chambers looked like," says Marsh. Textbooks showed them as something like large swimming pools, without detail.

Most geologists also believed that as the magma cools, crystals start to form throughout the body and eventually fall like snow to the floor of the chamber. The magma that remains is purified like a distillate. Eventually it was thought to cool into basalt, the fine-grained rock that underlies both seas and the continental granite.

But weaknesses in this model have always vexed Marsh. The model might hold if magma were similar to water, he says, in which case crystals would easily precipitate out of the solution. But magma is viscous. Crystals should logically get stuck in the goo, rather than settling out.

Marsh proposes that rather than looking like a swimming pool, a magma chamber is more like a series of chambers. Furthermore, rather than being injected into the one large vat, magma surges upward and then downward many times, in what Marsh calls a "mush column."

What's more, he says, rather than originating within the cooling magma as a precipitate, the crystals are actually transported up from great depths by the fast-flowing magma. Finally, the magma comes to rest, cools, and solidifies. Crystals (the largest are called phenocrysts) that were dredged up settle to form thick piles on the floor.

To test his hypothesis, for the past three years Marsh has traveled to Antarctica to a desolate region 800 miles from the South Pole. In this "geological paradise," says Marsh, 183-million-year-old sheets of magma formed cliffs known as sills. The bare, exposed rock harbors distinctive magmatic intrusions.

Some sills contain no phenocrysts, and are key to testing his hypothesis, says Marsh. Such structures were formed by magma that meandered upward at too leisurely a pace to pick up any phenocrysts. According to his theory, magma that is initially free of phenocrysts will remain relatively uniform and free of large crystals while it solidifies. In contrast, intrusions that were formed by fast-flowing magma, which dredged up crystals of various sizes and densities, should contain more complex chemical layers.

In addition, Marsh theorizes, whether phenocrysts are present or not, as magma cools, its margins become a mushy zone of crystallization, which he calls the solidification front. The mushy zone is heavier than the underlying magma, and eventually it tears open. Enriched magma seeps into the tears, and spreads out into a layer about two feet thick and 125 feet long. These layers are what eventually become the continental material.

On their most recent expedition, Marsh's team pried 1,700 pounds of rock out of the cliffs and shipped it back to Homewood. Using X-ray fluorescence, they are analyzing the chemical composition of various samples. The findings from this expedition and earlier ones support the hypothesis. Cliffs laden with phenocrysts have chemical strata whose chemical composition matches that predicted by Marsh's model. In contrast, cliffs lacking phenocrysts are essentially uniform from the base to the top. And every body has torn solidification fronts filled with continental-type material.

Marsh reported on his findings in the February 1996 Mineralogical Magazine. --MH

Written by Elise Hancock and Melissa Hendricks.

Gray matter of the sexes

Cognitive scientists consistently have found that women are generally better at verbal skills than are men. Is it because little girls start practicing earlier, making social talk at dolly tea parties, while the boys are out slinging Ninja spears? Or is some innate structure governing verbal ability stronger in females than it is in males? Many biologists would say that both nature and nurture are involved. However, a recent Hopkins study tips the balance toward the nature side of the equation.

Through magnetic resonance imaging of the brains of men and women, a team of psychiatrists found that two key regions of the brain involved in verbal fluency are significantly larger in women than in men. "Verbal ability might be more tied to genes than we thought," says Thomas Schlaepfer, an assistant professor of psychiatry and the study's lead investigator.

Schlaepfer's group measured the volume of gray matter in the brains of 17 women and 43 men. They then measured the percentage of gray matter in two brain regions tied to verbal ability: the dorsolateral prefrontal cortex, which is involved in language comprehension, particularly the emotional components of language; and the superior temporal gyrus, which is involved in spoken language (including foreign language skills). Since brain size varies widely throughout the population and tends to shrink with age, the scientists corrected for overall brain size and age in computing the percentages of gray matter.

MRI revealed that the language comprehension region was 23.2 percent larger in women than in men, and the spoken language region was 12.8 percent larger.

The next set of experiments may help to balance the brain equation of the sexes. The scientists plan to look at gray matter in the parietal lobe, which is tied to the ability to remember and work with numbers and to understand spatial relationships--skills at which men excel.

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