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NS 25 aug 2001

Nukes in the basement How would you like to live over a nuclear power plant? NS 25 aug 2001

A NUCLEAR reactor designed to generate power in the basement of an apartment block is being developed in Japan. In the past few months government-backed researchers have been testing a fail-safe mechanism for the reactor, which will close down automatically if it overheats.

The Rapid-L reactor was conceived as a powerhouse for colonies on the Moon. But at 6 metres high and only 2 metres wide this 200-kilowatt reactor could relatively easily fit into the basement of an office building or apartment block, where it would have to be housed in a solid containment building.

"In the future it will be quite difficult to construct further large nuclear power plants because of site restrictions," says Mitsuru Kambe, head of the research team at Japan's Central Research Institute of Electrical Power Industry (CRIEPI). 'To relieve peak loads in the near future, I believe small, modular reactors located in urban areas such as Tokyo Bay will be effective," he says. Kambe's research is being financed by the Japan's Atomic Energy Research Institute. Unlike normal nuclear reactors, the Rapid-L has no control rods to regulate the reaction. Instead, it uses reservoirs of molten lithium-6-an isotope that is effective at absorbing neutrons. The reservoirs are connected to a vertical tube that runs through the reactor core. During normal operation the tube contains an inert gas. But as the temperature of the reactor rises, the liquid lithium expands, compressing the inert gas and entering the core to absorb neutrons and slow down the reaction.

The lithium acts as a liquid control rod. And unlike solid control rods, which have to be inserted mechanically, the liquid expands naturally when the core gets warm. The Rapid-L uses the same principle to start up and close down the reaction. The reactor would be cooled by molten sodium and run at about 530 'C. Kambe's main concern now is to test the fail-safe system's long-term durability.

The research "is part of the effort being made in the US and in japan to develop reactors which do not need hardware to keep them safe," says John Gittus of the University of Plymouth. 'Rapid power plants could be used in developing countries where remote regions cannot be conveniently connected to the main grid,' says Kambe.

"The success of such a reactor depends on the acceptance of the public, the electricity utilities and the government," Kambe admits. But Malcolm Grimston, a nuclear expert at the Royal Institute of International Affairs, is sceptical that the Japanese people could be persuaded of the reactor's safety. "There's nothing wrong with the concept," says Grimston. "But if the Japanese public won't now accept big reactors for safety reasons, then you have to wonder what the response would be building lots of small reactors in the middle of cities." Peter Hadfield and Michael Fitzpatrick

Chaos rules In fact it's the secret to your brain's success

THE background chatter between brain cells isn't just random noise but structured chaos, says a team of scientists who have modelled brain activity. They say this could explain how subtle changes in our surroundings rapidly trigger complex mental images.

Chaotic activity may be unpredictable, but it is orderly and follows rules, unlike random noise. Its hallmark is the butterfly effect: a tiny change in the initial condi tions of a chaotic system will have a dra matic impact on the outcome. The existence of chaos in the brain could explain how we make sense of an ever changing world.

A popular alternative theory is that the brain acts like a computer, with individual neurons signalling to each other in a step wise fashion. But this may not explain how we form an impression of, say, a familiar smell without having to think about it first.

But researchers have had trouble finding clear evidence for chaos in the brain. In the latest attempt, neurobiologist David Liley at Swinburne University of Technology in Mel bourne and his colleagues built a mathe matical model of the cortex, the part of the brain that deals with memory, language and perception, and contains billions of neurons. The model is based on a set of equa tions that describe the average electrical potential between the outside and inside of the neurons under different conditions.

Liley and his team found that the model a: not only generated chaos, but also produced

a pattern very similar to the "alpha rhythm" that typically appears when someone closes their eyes and relaxes. He argues that the spontaneous appearance of the pattern suggests the model is mimicking what happens in the brain. 'The alpha wave is the sanity check," he says. 'It suggests that the chaos we get is also plausible." "A plus of [the team's] model is that it attempts to include real physiological quantities," says neuroscientist Scott Kelso of Florida Atlantic University in Boca Raton. But he remains sceptical about what it demonstrates. 'The model produces chaos, there's no doubt about that. But does that mean that chaos is the major dynamical feature of the nervous system? That's still an open question." It's likely to be a tough question to answer. The simulated brain activity produced by the model was very sensitive to change, becoming more or less chaotic depending on the input to the neurons. So it may not be possible to detect signs of chaos in actual brain recordings because researchers could never completely control all the inputs in a real person's brain. But the existence of chaos in the brain could be tested indirectly by using the model to predict how electrical activity in the brain responds to drugs. That could then be tested directly in living animals, says Liley. Rachet Nowak, Metbourne More at: Chaos ivot 11, p 474)

NS 7 Jul 2001

Birth of a miracle Soon you may not need eggs or sperm to have children of your own NS 7 Jul 2001

MEN and women who can't produce sperm or eggs could one day have 'natural" children of their own thanks to a form of cloning.

Gianpiero Palerino of Cornell University in New York has created artificial human eggs that contains just one set of a would-be mother's chromosomes. Such eggs could be fertilised with the partner's sperm, just like a normal egg.

And in Australia, Orly Lacham-Kaplan of Monash University in Melboume has shown that you can fertilise eggs, not with sperm, but with cells taken ftom elsewhere in the body. But there are still considerable obstacles to overcome before either technique could be used to create human babies.

The trouble is that we inherit not just genes, but chemical marks, or imprints, that turn some genes off. Chromosomes taken from body cells have different patterns of imprinting to egg and sperm cells, and that could cause developmental abnormalities. This may be why some clones have problems.

Because of the risks, adds Palermo, careful testing in animals and further understanding of how imprinting works are needed before the new methods are applied to humans. "It's something we are evaluating," he says. "We're just going one step at a time."

If the technique can be made safe, it would help the growing number of people who can conceive only with the help of donated eggs or sperm-and are therefore not genetically related to their children. Some women lose their eggs because of chemotherapy or ovarian surgery. But many women are also finding themselves in this situation because they've put off childbirth until it's too late. And although existing fertility treatments can help men with low sperm counts, they don't work for men who make abnormal sperm, or no sperm at all.

One solution would be cloning: transplanting genetic material from, say, a skin cell of the would-be mother or father into an egg from which the DNA has been removed. But because the baby would be identical to its parent, this technique is highly controversial and likely to be banned in many countries.

So Palermo and his colleagues are trying to use cloning techniques to create eggs that behave more as nature intended. Like normal cells in our body, a mature human egg usually has two sets of chromosomes-one inherited from the woman's mother, the other from her father. When the egg is fertilised, it retains one set in a so-called pronucleus, and spits out the rest in a little package called the polar body. The fertilising sperm, which contains just one set of chromosomes, then restores the full complement.

Palermo's team has mimicked this process by transplanting a nucleus from a body cell into a mature human egg that has had its genetic material removed. By prodding the reconstituted egg with a pulse of electricity, they can make the nucleus divide in half, forming two pronuclei (see Diagram). The team removes one pronucleus and then fertilises the egg by injecting a sperm.

So far, however, the resulting embryos have stopped developing after only one or two rounds of cell division, they told a conference on human reproduction in Switzerland this week. "This is preliminary work," cautions Palermo, "but at least in theory, it might be a way to provide eggs for sterile women." However, a child created this way would inherit the DNA-containing structures called mitochondria from the donor egg, and would thus effectively have three parents (see New Scientist, 12 May, p 7). Meanwhile, a related technique being being developed by Lacham-Kaplan and her colleagues might help infertile men. The team has succeeded in "fertilising" a normal mouse egg using a cell taken from the body of a male. This is surprising, because the body cell has two sets of chromosomes.

But the team found that when the egg is exposed to certain chemicals, it spits out two polar bodies. One, as normal, contains the egg's spare chromosomes. But the other contains half the chromosomes of the transplanted nucleus, leaving the fertilised egg with the usual two sets.

Even more surprising, such eggs go on to develop relatively normally in the lab, up to the pre-implantation stage. Lacham-Kaplan is now trying to transfer these embryos into surrogate mice. Claire Ainsworth

Utterly repulsive You've heard of fearsome black holes, but nothing as repellent as this

THREE years ago we discovered that the Universe is expanding at a faster and faster rate. Now physicists say this might mean the Universe is littered with invisible "anti black holes" that repel any matter that comes close. The accelerating expansion of the Universe has been very difficult to explain. Many theorists think its ballooning size is caused by an exotic material called "quintessence", a form of vacuum energy that pervades all of space and exerts a negative, outwards pressure (New Scientist, 3 April 1999, p 28). This is similar to the vacuum energy thought to have driven 'inflation", the rapid expansion of the Universe just after the big bang. But according to David Santiago of Stanford University in California, if quintessence exists it might be "clumpy" on small scales, just like normal matter. Although the Universe looks fairly smooth on large scales, planets, stars and galaxies make it patchy on small scales. "It's certainly plausible that quintessence has the same fingerprint," says Santiago. Arthur Chernin of Moscow University and Oulu University in Finland, along with Santiago and his Stanford colleague Alexander Silbergleit, decided to solve the equations behind general relativity, Einstein's theory of gravity, assuming that clumpy quintessence exists. The results suggest the Universe might contain a new class of object-anti black holes that repel matter rather than sucking it in.

Like black holes, they would be 'singurarities" exerting an infinite force on matter. The force of the singularity's antigravity would grow as you got closer, becoming infinitely strong at its centre. So nothing could get too close. 'Some of its properties are quite weird," says Santiago. 'If such an object exists, it will be protected by this 'force shield' and the singularity will be unreachable."

Anti black holes-in common with normal black holes-would be invisible, but they might be detectable because their gravity would make nearby matter and light move in unexpected ways. However, Santiago says that they may never have formed in the first place because their own antigravity might prevent them clumping together. "These objects very probably are unstable," he says. "It might depend on how strong their anti gravity is."

The team, which has sub mitted its results to Physics Letters A, is now trying to work out whether or not the anti black holes can form. If they can, they might be just one of a range of related exotic objects, including stars and galaxies, made of quintessence. 'One can let the imagination run wild and imagine all sorts of interesting non-standard scenarios," says Santiago.

He admits, however, that these oddities might turn out to be nothing more than a mathematical curiositiy. "Of all our results, this is prlbably the most likely to be just of academic interest," he says. "In order to be more definitive about their importance, we have some homework to do-we're working on it." Hazel Muir More at: http:Harxivorg/abs/astro-ph/0106144

Liquid genius How superchilled helium can tell us that the Earth's still tuming

JUST as the classic "two-slits" experiment shows that a beam of light is a quantum wave, a team of researchers has now done the same trick with a flowing liquid, showing that it, too, demonstrates quantum interference. Their experiment is so sensitive it can easily sense the turning of the Earth. In the classic demonstration of quantum interference, a light beam is split in two and recombined. If the two waves line up peak to peak, the recombined beam shines bright, but if peak lines up with trough they cancel out. Physicists have shown this in light, electricity and neutron and atom beams.

The latest material to show quantum interference is ultra-cold helium-3, a 'superfluid" that behaves like a quantum wave and flows without viscosity, sayj. C. S6amus Davis, Richard Packard and colleagues at the University of California, Berkeley.

To detect interference, the team made the liquid equivalent of a superconducting quantum interference device, or SQUID, which uses interfering electrical currents to detect tiny changes in magnetic fields. It consists of a superconducting ring with an input on one side and an output on the other. An incoming wave of electrons splits, flows through the two halves of the ring, and recombines on the far side.

Each half of the ring contains a constriction called a Josephson junction-a tiny sandbar that a quantum wave of electrons can barely slosh across. The junction accentuates the wave nature of the current. A magnetic field passing through the ring affects the current in the two halves of the ring differently, which changes the synchronisation of the recombining waves. A tiny increase in the field causes the two waves to line up peak-to-trough and the output drops to zero. A further increase causes the two waves to line up peak-to-peak, producing maximum output, and so on.

To make an analogous device for a liquid, the researchers fashioned a narrow tube into a loop roughly 1.4 centimetres in diameter and filled it with helium-3 cooled to less than 0.001 kelvin. For "Josephson junctions", they used delicate membranes pierced with 4225 holes 100 nanometers in diameter.

The researchers knew that rotation would affect their ring in the same way as a magnetic field affects a SQUID. The flow of helium should repeatedly swing to zero and back to its maximum value as they change the rate at which the ring rotates relative to free space. All they had to do to provide the rotation was to change its orientation relative to the Earth's axis. When they did this, the flow varied precisely as expected.

The result clinches a long-anticipated connection between superfluid helium and superconductivity, says William Zimmermann of the University of Minnesota in Minneapolis. "I attach a whole lot of importance to anything that makes things clear and convincing," he says. Adrian Cho More at: Noture ivol 412, p55)

Unleash the aliens We'll know when it's safe

ON THE eve of a major conference on the safety of genetically modified food and crops, two research teams have put forward their vision of how scientists can ensure that transgenic plants and animals don't run riot when released into the environment. "At the moment, the environment is being used as an open air laboratory," says Adrian Bebb of Friends of the Earth in Britain. There is no agreed way to evaluate the dangers of GMOs before field trials are carried out. Once an organism has been released, it could be too late. Now William Muir and his colleague Richard Howard at Purdue University in Indiana have developed a way to spot rogue GM organisms long before they are released into the environment. The technique could do for GMOs what clinical trials do for drugs. "Pharmaceuticals companies have to ensure that their drugs are safe for human consumption," says Muir. "Agricultural companies should have to ensure that their organisms are safe for the environment." His plea comes as delegates from OECD countries, the UN Food and Agriculture Organization and the World Health Organization prepare to meet in Bangkok on 10 July to thrash out a consensus on the science behind GMOs and the public's concerns. Muir and Howard hope their method will win enough support from scientists and regulators to be adopted worldwide. It is based on taking the results of extensive lab tests and feeding them into a computer model. This, they say, can predict whether a foreign gene would spread if a GM organism escaped or was released into the wild. So far Muir and Howard have only tried their model on fish, but in a paper published this week in The American Naturalist (vol 158, p 1), they say the same principle would work for apy animal or plant species. The model would give scientists common ground-something they can agree on, says Muir. "Once scientists are able to agree, that makes something much more acceptable to the public." Environmentalists have given the idea a cautious welcome. "It would help," says Bebb. 'I do think there's a need for research like this before experiments come out of the lab." Sue Mayer of GeneWatch UK agrees. "Models are extremely useful and they can really pick up what things are sensitive to. They are bound to make you feel that there has been rigorous investigation before you go to the next step." But models are only ever as good as the data you put in, she warns.

But what will the biotech companies think? "I suspect that industry would baulk at such a thorough approach," says Peter Kareiva, a senior ecologist at the US National Marine Fisheries Service. It could take up to five years to get enough data on GM salmon strains for the model to work, for example. But Mayer says that firms won't have a choice if regulators deem such tests appropriate.

To develop their model, Muir and Howard identified six aspects of the life history of fish that affect their "fitness"-the number of offspring they produce. These include how many fish survive to adulthood, the age at which they sexually mature and the number of eggs females produce. Then they developed a computer model based on these six traits that predicts how any modified strain would fare against the wild-type fish. The researchers applied their model to a strain of Japanese ricefish, or medaka, to which they had added the gene for human growth hormone. They counted and measured separate populations of modified and unmodified fish for around two years to see how they compared.

The modified fish were less likely to survive to adulthood, but they reached sexual mat urity earlier and the females laid more eggs. Attempting to predict how these effects bal ance out would be extremely difficult, but the computer model can work it out.

Muir and Howard found that even though the modified fish were more likely to die young, they would still take over the natural population if released into the wild-so this should never be done. 'There's an ass umption that if juvenile viabil ity is lower, then the gene won't spread," says Muir. 'That's the common misconception that everybody's been working with. But we've shown that there are several other factors that can offset this."

"It is a sensible approach," says James Bullock of the Cen tre for Ecology and Hydrology in Dorset. "Modelling and lab based stuff only give a limited picture, but it gives you an idea of what may happen.

If anything, the model should overestimate the risks of GMOs in the wild, says Muir. 'We con sider the lab to be more benign and hospitable than nature," he says. "So if in the lab, transgenic organisms are not found to be a risk when they are given a beneficial environment, we feel confident that in nature there will be even less of a risk."

But John Beringer, former head of Britain's Advisory Committee on Releases to the Environment, disagrees. 'I don't believe that we know enough about fitness for that to be valid, " he says. "We don't know which characteristics are important because environments change so much."

While Muir is working out the risks of foreign genes spreading in the wild, Bullock

is trying to estimate the consequences of such contamination. He's using a technique called matrix modelling to combine data obtained from natural plants in the wild and from related GM crop species in the lab. This model predicts whether wild plants that gain foreign genes from their GM relatives would be likely to invade habitats at the expense of native strains. "We're saying: what if gene flow has already happened, what would be the consequences of that?"

He is measuring life-cycle traits such as seed germination, seed production and the survival rate of native plants in different habitats in the wild. His model uses these to calculate how fast their populations are increasing. He then does the same for GM plants grown in the lab. From this, he hopes to be able to tell whether a foreign gene will make wild plants more invasive or not.

Bullock hasn't published his results yet, and acknowledges that modelling can't give definite answers. But his initial results indicate that GM oilseed rape could affect its wild turnip relatives. In one worst-case scenario, a population of turnips could increase hugely at the expense of other species if it took up an oilseed rape gene that boosts seed production, he says.

The results could be used to help decide which GM plants are safe enough for field trials, Bullock says. "If you then put a plant into the wild, you could be fairly sure what the problems are likely to be."

The researchers accept that modelling environmental effects doesn't take into account other factors, such as ethical considerations, possible threats to human health and the potential benefits of the modified animals and plants. But Muir says he hopes his work will help make biotechnology more acceptable. Joanna Merchant