- Email: [email protected]
Antimatter molecule could lead to ultra-powerful laser
NASA/JPL
IT HAS a mere dribble of water compared to Earth, yet over the past few million years Mars has experienced periodic ice ages that have shaped layers of ice lurking beneath its dusty surface. The ice cycle arises from periodic fluctuations in its orbit similar to those that cause Earth’s climate to vary from ice age to interglacial. There are important differences, though, because with no large moon to stabilise it, the Red Planet’s tilt has varied far more widely than Earth’s. As recently as 5 million years ago, Mars’s axis wobbled between 25 and 45 degrees from the perpendicular to the plane of the solar system – enough to evaporate polar ice caps and precipitate snow on the equator. It then shifted to a low-tilt mode, tipping back and forth every 125,000 years in a range from 15 to 35 degrees. To see how this affected Mars’s ice, Norbert Schörghofer of the University of Hawaii modelled its sublimation and diffusion, starting 5 million years ago with an ice sheet covered by a layer of 15 per cent dust and 85 per cent ice. While warm spells sublime the ice, each of the 40 cold intervals caused diffusion of moisture into soil, where it freezes. The model results match the distribution of ice at mid-latitudes, suggesting that it diffused there within the past half-million years. Ice within about 15 degrees of the poles is much older, Schörghofer says (Nature, vol 449, p 192).
www.newscientist.com
Thanks for the memories, but how do you keep them? HOW do we store so many memories? It is a question that has puzzled neuroscientists for decades – and now it seems that our concept of how memory works may have been wrong all along. It was originally assumed that the number of memories was proportional to the number of neurons in a network. Given that even 1 cubic centimetre of the brain’s cortex contains about 50 million neurons, it seemed that the brain could indeed store masses of information. However,
this model relied on the notion that each neuron is connected to every other neuron, whereas a neuron is actually connected to between 5000 and 10,000 others. Neuroscientists then proposed that the number of memories was proportional to the number of connections per neuron. Now Yasser Roudi and Peter Latham at University College London have found a problem with this model too. They calculated that even with 10,000 connections per neuron, a network could only store about 100 memories –
regardless of how many neurons were in the network (PLoS Computational Biology, DOI: 10.1371/journal.pcbi.0030141). This implies that to store a large amount of information, the brain would have to use multiple networks. This may be problematic for something like vocabulary, Latham says. “You wouldn’t want to store 100 words in each of [many] different networks; you probably want to store them more or less in one place. Now we don’t know how [the brain] does this.” MARIA STENZEL/NATIONAL GEOGRAPHIC
The ebb and flow of Martian ice
Gamma-ray laser with extra punch AN EXOTIC molecule built from electrons and antimatter is being touted as a route to powerful gamma-ray lasers. An electron can hook up with its antiparticle, the positron, to form a hydrogen-like atom called positronium (Ps). It survives for less than 150 nanoseconds before it is annihilated in a puff of gamma radiation. It was known that two positronium atoms should be able to bind together to form a molecule, called Ps2, and now David Cassidy and Allen Mills from the University of California, Riverside, have made that happen. First, they trapped positrons in a thin film of porous silica. Those positrons captured electrons to form positronium atoms, and the pattern of decay rates signalled that some of these atoms had teamed up to form Ps2 (Nature, DOI: 10.1038/nature06094). If positronium atoms could be forced to merge into a kind of “super-atom” condensate, it would decay in bursts of identical gamma rays, which could lead to gamma-ray lasers a million times more powerful than standard lasers. “It’s like comparing a chemical explosion with a nuclear explosion,” Cassidy says.
Honey makes life a little bit sweeter PERHAPS Winnie the Pooh knows something we don’t. Honey could soon be marketed as a way to combat the effects of ageing. Lynne Chepulis and Nicola Starkey of the University of Waikato in Hamilton, New Zealand, raised rats on diets containing 10 per cent honey, 8 per cent sucrose, or no sugar at all for 12 months. The rats were two months old at the start of the trial, and were assessed every three months using tests designed to measure anxiety and spatial memory. Honey-fed rats spent almost twice as much time in the open sections of
an assessment maze than sucrose-fed rats, suggesting they were less anxious. They were also were more likely to enter novel sections of a Y-shaped maze, suggesting they knew where they had been previously and had better spatial memory. “Diets sweetened with honey may be beneficial in decreasing anxiety and improving memory during ageing,” says Starkey, whose work was funded by Fonterra, a dairy company interested in sweetening yoghurt with honey. She suggests the findings may be due to the antioxidant properties of honey, which have previously been demonstrated in humans. The results were presented at the Association for the Study of Animal Behaviour meeting at Newcastle University, UK, last week.
15 September 2007 | NewScientist | 23
IT HAS a mere dribble of water compared to Earth, yet over the past few million years Mars has experienced periodic ice ages that have shaped layers of ice lurking beneath its dusty surface. The ice cycle arises from periodic fluctuations in its orbit similar to those that cause Earth’s climate to vary from ice age to interglacial. There are important differences, though, because with no large moon to stabilise it, the Red Planet’s tilt has varied far more widely than Earth’s. As recently as 5 million years ago, Mars’s axis wobbled between 25 and 45 degrees from the perpendicular to the plane of the solar system – enough to evaporate polar ice caps and precipitate snow on the equator. It then shifted to a low-tilt mode, tipping back and forth every 125,000 years in a range from 15 to 35 degrees. To see how this affected Mars’s ice, Norbert Schörghofer of the University of Hawaii modelled its sublimation and diffusion, starting 5 million years ago with an ice sheet covered by a layer of 15 per cent dust and 85 per cent ice. While warm spells sublime the ice, each of the 40 cold intervals caused diffusion of moisture into soil, where it freezes. The model results match the distribution of ice at mid-latitudes, suggesting that it diffused there within the past half-million years. Ice within about 15 degrees of the poles is much older, Schörghofer says (Nature, vol 449, p 192).
www.newscientist.com
Thanks for the memories, but how do you keep them? HOW do we store so many memories? It is a question that has puzzled neuroscientists for decades – and now it seems that our concept of how memory works may have been wrong all along. It was originally assumed that the number of memories was proportional to the number of neurons in a network. Given that even 1 cubic centimetre of the brain’s cortex contains about 50 million neurons, it seemed that the brain could indeed store masses of information. However,
this model relied on the notion that each neuron is connected to every other neuron, whereas a neuron is actually connected to between 5000 and 10,000 others. Neuroscientists then proposed that the number of memories was proportional to the number of connections per neuron. Now Yasser Roudi and Peter Latham at University College London have found a problem with this model too. They calculated that even with 10,000 connections per neuron, a network could only store about 100 memories –
regardless of how many neurons were in the network (PLoS Computational Biology, DOI: 10.1371/journal.pcbi.0030141). This implies that to store a large amount of information, the brain would have to use multiple networks. This may be problematic for something like vocabulary, Latham says. “You wouldn’t want to store 100 words in each of [many] different networks; you probably want to store them more or less in one place. Now we don’t know how [the brain] does this.” MARIA STENZEL/NATIONAL GEOGRAPHIC
The ebb and flow of Martian ice
Gamma-ray laser with extra punch AN EXOTIC molecule built from electrons and antimatter is being touted as a route to powerful gamma-ray lasers. An electron can hook up with its antiparticle, the positron, to form a hydrogen-like atom called positronium (Ps). It survives for less than 150 nanoseconds before it is annihilated in a puff of gamma radiation. It was known that two positronium atoms should be able to bind together to form a molecule, called Ps2, and now David Cassidy and Allen Mills from the University of California, Riverside, have made that happen. First, they trapped positrons in a thin film of porous silica. Those positrons captured electrons to form positronium atoms, and the pattern of decay rates signalled that some of these atoms had teamed up to form Ps2 (Nature, DOI: 10.1038/nature06094). If positronium atoms could be forced to merge into a kind of “super-atom” condensate, it would decay in bursts of identical gamma rays, which could lead to gamma-ray lasers a million times more powerful than standard lasers. “It’s like comparing a chemical explosion with a nuclear explosion,” Cassidy says.
Honey makes life a little bit sweeter PERHAPS Winnie the Pooh knows something we don’t. Honey could soon be marketed as a way to combat the effects of ageing. Lynne Chepulis and Nicola Starkey of the University of Waikato in Hamilton, New Zealand, raised rats on diets containing 10 per cent honey, 8 per cent sucrose, or no sugar at all for 12 months. The rats were two months old at the start of the trial, and were assessed every three months using tests designed to measure anxiety and spatial memory. Honey-fed rats spent almost twice as much time in the open sections of
an assessment maze than sucrose-fed rats, suggesting they were less anxious. They were also were more likely to enter novel sections of a Y-shaped maze, suggesting they knew where they had been previously and had better spatial memory. “Diets sweetened with honey may be beneficial in decreasing anxiety and improving memory during ageing,” says Starkey, whose work was funded by Fonterra, a dairy company interested in sweetening yoghurt with honey. She suggests the findings may be due to the antioxidant properties of honey, which have previously been demonstrated in humans. The results were presented at the Association for the Study of Animal Behaviour meeting at Newcastle University, UK, last week.
15 September 2007 | NewScientist | 23