Davis and his colleague Richard Packard were working with helium-3, the
isotope with two protons and one neutron, cooled to a thousandth of a degree
above absolute zero (−273 °C). At this temperature, the helium is a
superfluid—that is, all of its atoms are in the same quantum state and
they move in lock step, with zero viscosity. This leads to such strange
behaviour as the fluid climbing up the sides of containers.

The researchers were trying to confirm what happened when two compartments of
superfluid helium at different pressures were linked up by narrow channels. If
the helium was a normal liquid, it would be expected to flow from the
high-pressure side to the lower pressure side. In the 1960s, however, the Nobel
laureates Philip Anderson, Brian Josephson and Richard Feynman had independently
predicted that a superfluid would oscillate back and forth between the
compartments at a frequency that is dependent on the pressure difference between
them.

To test this, Davis and Packard separated two compartments of superfluid
helium at slightly different pressures by a thin silicon nitride membrane with
several thousand tiny holes through it, each just a ten-millionth of a metre
across. Near the membrane, they placed a sensitive microphone.

In this week’s Nature (vol 388, p 449), the researchers say that
they heard the vibrations created by the helium sloshing back and forth several
thousand times a second. The whistling noise changed pitch as the helium
pressures changed, Davis says.

Researchers have recognised for some time that the intricate branching
structures of river networks are self-similar—that is, their structures
appear much alike on very different scales. “If you looked at a river on a map,
you wouldn’t be able to tell if you were looking at a scale of 1 kilometre or
hundreds of kilometres,” says Jon Pelletier of Cornell University in Ithaca, New
York.

This self-similarity, which is the hallmark of fractal systems, is also
evident in the land surrounding a river system. The ups and downs of a continent
are mirrored by the hills and valleys of a country. żěèśĚĘÓĆľs have offered
various explanations for why topography should be fractal but none has been
completely satisfactory, says Pelletier.

Now, using an approach that works from the bottom up, Pelletier has come
up with a new explanation. “About the only thing we know for sure about the
evolution of topography is what happens on a small scale,” he says. For example,
geologists have a good picture of how fault scarps created by earthquakes change
over time. When the ground on one side of a fault is pushed up relative to the
ground on the other side, it creates a steep incline with sharp corners at the
bottom and top.

Over time, as water flows over this scarp, it carries soil from the top edge
to the base, rounding both edges. This transformation and other small-scale soil
displacements are explained very well by the so-called diffusion equation for
sediment transport, says Pelletier. But, he adds, “no one has ever made any
connection between this fundamental observation and anything about
łŮ´Çąč´Ç˛ľ°ů˛šąčłó˛â”.

Pelletier has now combined the diffusion equation with a mathematical
description of how the amount of water available to move soil varies with
location. In places touched by only a few small streams, little water flows and
landscape changes occur slowly. By contrast, in areas where large rivers run the
topography evolves quickly.

This interplay, in which topography determines water flow and water flow
changes topography, produces the complicated patterns characteristic of river
systems and the land around them, says Pelletier. “You can take this simple
model and get very realistic river basins.” He has tested his model against
seven different places, ranging from river basins in the Himalayas to the
Mississippi River Valley, and found that its predictions agree quite well with
the real thing.

Pelletier, who has submitted his results to the Journal of Geophysical
Research, says the model also predicts what every hill walker already
knows—that land in lower areas tends to be relatively flat compared with
land at higher altitudes. “In the lowlands you have the largest rivers in the
system,” he says. And so, on average at least, a point in the lowlands will have
more water passing over it—and more soil carried off—than points
higher up.

“Any sort of irregularity in the lowlands topography is not going to last
long,” Pelletier adds. But variations in the highlands tend to stick around. Of
course, even lowlands can be quite hilly in places, Pelletier notes. But in his
models the smallest feature is about 100 metres across, and at this scale rivers
do keep the low elevations reasonably flat.

Quantum cryptographers have long sought techniques that can be proved to be impervious to tampering or eavesdropping, says Richard Hughes of Los Alamos National Laboratory in New Mexico. One such “provably secure” method is quantum key distribution, in which the key to a code is sent as a pattern of photons, which any eavesdropper will be bound to disturb.

Recently, researchers have focused on a second technique, quantum bit commitment, which would let people compare or combine information while keeping each individual’s contribution secret. This could be used, for example, to carry out dealings on the stock market without anyone being able to learn what others had bid.

Quantum bit commitment seemed to offer the best hope for doing this, says Dominic Mayers of Princeton University. Suppose Alice writes down a bit—a 0 or a 1—on a piece of paper, locks it in a box, and gives the box to Bob. She has committed herself to a choice, but he cannot know what her choice is until she provides the key.

The quantum version of bit commitment relies upon the way that polarised photons are received by filtered detectors. If Bob’s detector is set up to see only vertically polarised photons, it will respond with a 1 for each vertically polarised photon and a 0 for the horizontally polarised ones. Its response to diagonally polarised photons will be completely random. Similarly, if he sets his detector to see photons polarised on one of the diagonals, it will record a 0 for a photon on the other diagonal, and will respond randomly to horizontally or vertically polarised photons.

Alice can send a “bit in a box” to Bob by transmitting a string of photons that are all polarised horizontally/vertically, or all polarised diagonally. Bob, who has no way of telling how Alice polarised the photons, randomly sets his receiver sometimes for horizontal/vertical detection and sometimes for diagonal detection.

Bob randomly changes the setting and records a meaningless string of 0s and 1s. His polariser will record the true code only when its orientation matches Alice’s. Alice can prove that she chose, say, diagonal polarisation, by telling Bob what pattern of 0s and 1s he saw when his detector was on the diagonal setting.

The weakness, Mayers says, is that Alice can cheat by creating pairs of photons with matching polarisations and sending one in each pair to Bob while storing the second for later observation. Such matched photons have the strange quantum property that an observation of one affects how the other will appear to a detector. Using this trick, Alice can in effect create two linked locked boxes, send one to Bob, and determine what appeared in Bob’s box by fiddling with her own.

Researchers knew this was a weakness of some quantum bit commitment schemes. “But I realised it was a general principle,” says Mayers. His proof appears in Physical Review Letters (vol 78, p 3414), along with a closely related paper by physicists in Britain and Hong Kong, showing that no quantum bit confinement scheme is completely secure. “It’s sad that we lost it,” Mayers says.

It has long been known, for instance, that the heavier an animal ,the more
slowly it breathes. Respiratory rate is inversely proportional to body mass
raised to the power 1/4. And in all organisms the metabolic rate—the
amount of energy used to sustain life—is roughly proportional to body mass
raised to the power 3/4. It is not obvious why this should be, notes team member
Geoffrey West of Los Alamos National Laboratory. At first glance it seems that
organisms’ energy use should grow in proportion to body mass itself, not some
power of it.

In last week’s issue of Science (vol 276, p 122) the team proposes a
model that explains several dozen such scaling laws. Noting that all organisms
need systems to distribute resources around the body—circulatory systems
in mammals, tracheal tubes in insects, vascular systems in plants, and so
on—the researchers made three assumptions.

First, in order to reach every part of an organism, a system must be a
branching, fractal-like network that fills the whole body. Second, the terminal
branches of a particular type of network—capillaries in a circulatory
system, for instance—are the same size in all organisms. And third,
evolution has tuned the networks to minimise the energy needed to deliver the
goods. So a circulatory system should make a heart work no harder than necessary
to send blood around the body.

When the researchers analysed the consequences of these rules mathematically,
they found exactly the same scaling laws as observed in the real world. “When we
put all this together,” says West, “to my utter amazement, out came these
quarter powers.” The researchers found that they could predict more than a dozen
scaling laws dealing with circulatory systems, such as heart rate and the size
of the aorta.

The results explained a similar number of scaling laws for respiratory
systems. And, since metabolic rate is closely related to factors like the amount
of oxygen transported by the circulatory system, the researchers were also able
to calculate that, as observed, metabolism should increase in proportion to body
mass raised to the 3/4 power.

William Calder, an ecologist at the University of Arizona, says that the
theory is the best explanation to date. “It’s beautiful,” he says. “This is the
most promising thing that has come along—it’s the only thing in town that
ˇÉ´Ç°ů°ě˛ő.”

West’s colleagues, James Brown and Brian Enquist of the University of New
Mexico, hope to extend the model from individuals to ecological systems. “Many
ecological phenomena also scale with quarter powers,” Brown says, including life
span and duration of pregnancy in mammals.

Michael Ullman of Georgetown University in Washington DC and his colleagues
began their work by testing the language skills of a group of 24 patients with
Alzheimer’s disease. They found that their subjects had particular difficulty
with irregular verbs. A subject might, for instance, correctly give “chopped” as
the past tense of “chop” but then stumble when asked about “dig”.

That was not completely surprising, notes Ullman—knowing that “dug” is
the past tense of “dig” is a feat of memory, which is poor in Alzheimer’s
patients. But the real surprise came when the researchers compared these
subjects with 45 people suffering from Parkinson’s or Huntington’s disease. They
had no trouble with “dug” or “swam”, but struggled when the past tense was
formed simply by adding “ed”.

Ullman says that the language difficulties of the Parkinson’s and
Huntington’s patients were reminiscent of their physical disabilities.
Huntington’s patients, who suffer from uncontrollable movements, tended to use
runaway words—saying “lookeded” instead of “looked”, for example.
Parkinson’s patients, who have difficulty using some muscles, were more likely
to leave off the “ed” altogether and say “look”.

The researchers claim in the latest issue of the Journal of Cognitive
Neuroscience (vol 9, p 289) that all this hints at how the human brain
handles language. They suggest that word memory relies on areas of the brain
that are responsible for “declarative memory”, the memory of facts and events,
which is damaged by Alzheimer’s. But the rules of grammar are processed by
sections of the brain that handle “procedural memory”. This type of memory is
used in physical activities such as lifting an arm—abilities sabotaged by
Huntington’s and Parkinson’s.

“This has been a big argument in linguistics for years,” says psychologist
Michael Gazzaniga at Dartmouth University in Hanover, New Hampshire. In the
debate over the importance of grammar rules versus rote memorisation, some
scientists have contended that language is mostly memory-driven. But Gazzaniga
says that the new findings “indicate strongly that both processes are at
ˇÉ´Ç°ů°ě”.

“It should really help us understand language,” says Ullman. In a follow-up
study presented at a conference last week, he reported that men are more likely
than women to have difficulty with regular verbs after diseases that damage the
procedural memory. But both have problems forming the past tense of made-up
words such as “spuff” (“spuffed”). This suggests, says Ullman, that women store
more words in memory than men, and fall back on the rules only when presented
with unfamiliar words.

Although some techniques, such as laser fluorescence, can pick out a single
molecule, they do not say much about its structure. To work this out, scientists
have always had to gather data from thousands of molecules at a time. Now,
however, a team at the Massachusetts Institute of Technology has managed to pick
out lone molecules and pinpoint their structures.

To pull off this trick, the team focused a laser beam on a spot in a solution
containing silver particles about 100 nanometres across. Attached to the surface
of some of these particles was a single dye molecule. The researchers ensured
that there were so few of these molecules that only one would lie in the path of
the laser beam at any given time.

When the photons from the laser strike a dye molecule, they jiggle its atoms
and make it vibrate. The wavelengths of light that rebound from the molecule
under these conditions depend on the ways that the molecule vibrates. This in
turn depends on the arrangement of the chemical bonds that hold it together.
“Each molecule has a vibrational fingerprint,” explains team leader Katrin
Kneipp of the Technical University of Berlin, a visiting professor at MIT. By
analysing the spectrum of the photons that bounce back from the molecule, the
researchers could identify it.

Raman scattering, as this method of looking at molecules is known, has been
used for decades. But usually each molecule scatters so few photons that
trillions of them are needed to create a signal strong enough to detect. About
twenty years ago, scientists realised that they could enhance the signal by
anchoring the molecules to a rough silver surface, for unknown reasons. At the
time, no one realised how great that enhancement could be.

Kneipp found that the number of photons produced is enhanced by a factor of
10¹⁴ (Physical Review Letters, vol 78, p 1667). Earlier studies had
missed this because they looked at the average behaviour of large collections of
molecules, in which only a few molecules might have produced a huge number of
photons while the rest did nothing.

The researchers, from institutions in Georgia, Maryland and the District of Columbia, exposed slices of tissue from rats’ brains to periodically varying electrical fields, which peaked several times a second. Each tissue sample contained a network of between 500 and 1000 interconnected neurons, explains physicist William Ditto from the Georgia Institute of Technology in Atlanta.

When the electrical field peaked beyond a certain threshold, the network of neurons would respond to it by generating a series of electrical pulses in sync with the applied field. But when the field was below the threshold, the neurons could not detect the electrical signal and no pulses appeared.

However, Ditto says, the neurons responded to a sub-threshold signal if the researchers added a bit of “noise”—a randomly fluctuating electrical field—to the mix. Although it could be expected that the noise would make it even more difficult for the neurons to detect the weak signal, the result was the opposite.

This effect is known as “stochastic resonance”, says Mark Spano of the Naval Surface Warfare Center in Maryland, another member of the team. It has been found in various physical systems, such as electronic circuits, as well as in living creatures.

In March, for instance, researchers at the University of California, Berkeley, reported that crickets use stochastic resonance in their cercal systems, which sense air disturbances. And last month, scientists in Boston showed that stochastic resonance enables people to feel pressure on their fingertips that would otherwise be too faint to detect.

But until now, Spano says, no one had seen stochastic resonance at work in networks of neurons from the brain. His group’s experiment shows that electrical noise can increase the sensitivity of neurons to a weak signal by, in essence, pushing the neurons closer to their threshold. The results were published last week in Physical Review Letters.

The molecule was named after Richard Buckminster Fuller, an architect who
explored similar shapes in “geodesic” domes made from glass and metal. But the
full name never stuck. As far as the world is concerned, the carbon spheres are
buckyballs. They have since spawned a new branch of chemistry. But it all began
as an unexpected blip in an experiment designed to study the sorts of carbon
molecules that form near stars.

At Rice University in Houston, Texas, Smalley had developed a unique machine
that vaporised small pieces of material using a laser and swept the resulting
plasma along in a high-speed stream in which molecules and clusters of varying
size would form. In 1984, Kroto, who works at the University of Sussex in
Brighton, heard about the machine, and was invited to visit Houston by Smalley’s
colleague Curl.

When he arrived, Kroto realised that the machine was just what he needed for
his studies of the formation of carbon molecules in interstellar space. Smalley
and Curl were reluctant to interrupt their own research. But Kroto was
insistent, and in August 1985, the two American researchers relented. “We wanted
to satisfy Harry Kroto and get him out of the lab,” jokes Smalley.

After several days of vaporising graphite, the chemists had found the long
chains of carbon atoms that Kroto was looking for, but they had also discovered
something else. The machine was producing large amounts of clusters with exactly
60 carbon atoms. “We were just fascinated by the signal for this molecule C
₆₀,” Kroto says. “We wondered what this peak was.”

The chemists had little information about the mystery molecule. They knew its
size and that it was both extremely stable and reluctant to react with anything
else. The crucial breakthrough came when they realised that these properties
stemmed from the now-famous soccer ball shape, technically known as a truncated
icosahedron. The three chemists thought that the molecule was probably
spherical, since any loose edges would offer sites with which other molecules
could react. But they could not understand how 60 carbon atoms would be arranged
to form such a ball.

Days of brainstorming followed, until Smalley, working late one night, built
a paper model with all the right properties. Kroto, however, has long insisted
that he had described this structure to the group the day before. Partly due to
the tension created by these conflicting claims, the collaboration eventually
ended. But both sides now want to put the dispute behind them. “We’ll agree to
disagree forever,” says Smalley. “As far as I’m concerned, a rift doesn’t exist
any longer,” adds Kroto.

What does exist is a booming field of chemistry. In 1990, researchers led by
Wolfgang Krätschmer of the Max Planck Institute for Nuclear Physics in
Heidelberg and Donald Huffman of the University of Arizona in Tucson discovered
a simple way to make buckyballs in large quantities, confirming the structure
outlined by Curl, Kroto and Smalley. Since then, scientists have doped
buckyballs with various elements to create superconductors. They have used
buckyballs as cages to enclose atoms, and have learned to modify the buckyball
production process to make swollen spheres with many more than 60 carbon atoms.
They can even create “buckytubes”—long cylinders of carbon atoms that
could be used in superstrong composite materials. Today, the simple 60-atom
spheres seem almost passĂŠ.

Given this explosion of activity, the three buckyball pioneers had been seen
as favourites for a Nobel prize. Which may explain Kroto’s laid-back response to
the award. He picked up the news on the Internet, but decided to pop out for a
quiet lunch before dealing with the inevitable avalanche of congratulations and
media enquiries. “I decided lunch was more important,” he says.