[naturenews] from [nature.com]
[naturenews]
Published online 27 September 2009 | Nature | doi:10.1038/news.2009.953
News
Physicists shrink X-ray source
Laser accelerator almost fits on a tabletop.
By Geoff Brumfiel
A team of physicists has built a small, powerful X-ray source — a prototype of the sort of machine they hope could replace much larger facilities.
The technology has the potential to revolutionize everything from microbiology to materials science by giving scientists easier access to high-quality images of the things they are studying.
Researchers use X-rays to probe all manner of things — from comet dust to fossilized animals trapped in amber. But making high-quality images requires much brighter and better controlled sources than those available in most institutions. So at the moment, most scientists use large particle accelerators known as synchrotrons, which work by accelerating electrons around a ring. As the electrons bend along the circular path, they naturally emit high-quality X-ray radiation.
Synchrotrons are large, costly and usually in high-demand by scientists, so Matthias Fuchs of the Max-Planck-Institute for Quantum Optics in Garching, Germany, and his colleagues have been working on another way to generate electrons.
Rather than using conventional magnets to guide and accelerate electrons, the team used a powerful laser beam and a small cell of hydrogen gas. They shot a brief, 37-femtosecond (10-15 seconds) pulse into the cell to blow the electrons off the hydrogen atom's nuclei. But electrical attraction causes the electrons to snap back towards the positive ions, so for a brief period after the pulse the electrons vibrate back and forth around the hydrogen atom's positive core, producing a wave. As they do so, a few electrons break loose and ride the crest of the electron wave. "Just like a surfer, the electrons can surf down these waves," Fuchs says.
The electrons then sail through a series of magnetic lenses, which feed them into a second series of magnets that cause them to wiggle back and forth — releasing low-energy 18-nanometre wavelength X-rays as they go.
Short pulse
Because the electric fields between the hydrogen ions and their electrons are so large, the electrons pick up speed much more rapidly than they would in a conventional accelerator. That means a machine the size of a building can be shrunk to the size of a tabletop. Well, almost. Fuchs says that including the laser, the accelerator takes up two fairly large tables. "We came up with the phrase 'banquet tabletop'," he says. The team's research has been published by Nature Physics1.
Nevertheless, "it is exciting", says Tom Katsouleas, dean of engineering at Duke University in Durham, North Carolina. Other groups had already shown lower-power radiation from similar systems, so it wasn't surprising, he adds. "I don't think anybody really doubted it could be done." "But they've actually shown that the beam quality can be fairly high," he says.
Because relatively few electrons are accelerated, the pulses are bright but short, so the 'tabletop' accelerator is unlikely to replace conventional synchrotrons any time soon. Still, Katsouleas says, there is no reason, in principle, why they could not be made into a workable X-ray source for use in universities.
References
1. Fuchs, M. et al. Nature Phys. advance online publication doi:10.1038/NPHYS1404 (2009).
[naturenews]
Published online 27 September 2009 | Nature | doi:10.1038/news.2009.954
News
Sex chromosomes linked to evolution of new species
Questions over conflict of the sexes remain.
By Natasha Gilbert
Experiments in stickleback fish have shown for the first time that the evolution of new sex chromosomes is the driving force behind the formation of a new vertebrate species.
Up until now, most evidence has shown that new species arise because they have adapted to new environments. But a study to be published by Nature1 found that the emergence of new sex chromosomes caused a population of threespine stickleback fish in the Japan Sea, to diverge from its Pacific Ocean–dwelling ancestor (Gasterosteus aculeatus) — creating a new species.
Jun Kitano, an evolutionary biologist at Tohoku University in Japan, and his team discovered that the Japan Sea stickleback fish had different sex chromosomes compared to their ancestors. The ancestral Y sex chromosome (which makes males) had fused with a non–sex chromosome to create a new sex chromosome in the Japan Sea stickleback fish.
The team also observed that the Japan Sea males exhibited more aggressive mating behaviours than their ancestral populations. Females from the ancestral population avoid mating with the Japan Sea fish due to their more aggressive behaviour. And in lab tests, the male progeny of the two populations were sterile.
The study found that the gene responsible for the aggressive mating behaviour of the Japan sea males was on the new Y chromosome. The new mating behaviours linked to the new sex chromosome stop the two populations from mating, making the Japan Sea population a new species.
"There is a gene on the new sex chromosome that causes differences in mating behaviour in the male stickleback. This behaviour leads to evolution of a new species of stickleback," says Catherine Peichel, a molecular biologist at the Fred Hutchinson Cancer Research Center in Seattle, Washington, and a member of the research team that published the study.
Battle of the sexes
Ole Seehausen, a fish ecologist and evolutionist at the Swiss Federal Institute of Aquatic Science and Technology in Dübendorf, says the study is "remarkable". "This is the first study that has shown a direct link between the evolution of sex chromosomes in vertebrates and the evolution of a new species," he says.
Peichel says that not much is known about what drives the evolution of new sex chromosomes. Scientists have hypothesized that conflict between the sexes could be behind this. If species carry genes that could be advantageous to males but detrimental to females, then natural selection will favour that these genes be located in the part of the genome that appears in males but not in females.
"A good place for them to be is right next to the gene that causes sex determination," says Peichel.
However the study has not yet answered whether conflict between the sexes drives the evolution of new sex chromosomes. "They do not prove that there is sexual conflict over the trait they study — that is that it is good for males but not females," Seehausen says.
References
1. Kitano, J. et al. Nature doi:10.1038/nature08441 (2009).
[naturenews]
Published online 27 September 2009 | Nature | doi:10.1038/news.2009.953
News
Physicists shrink X-ray source
Laser accelerator almost fits on a tabletop.
By Geoff Brumfiel
A team of physicists has built a small, powerful X-ray source — a prototype of the sort of machine they hope could replace much larger facilities.
The technology has the potential to revolutionize everything from microbiology to materials science by giving scientists easier access to high-quality images of the things they are studying.
Researchers use X-rays to probe all manner of things — from comet dust to fossilized animals trapped in amber. But making high-quality images requires much brighter and better controlled sources than those available in most institutions. So at the moment, most scientists use large particle accelerators known as synchrotrons, which work by accelerating electrons around a ring. As the electrons bend along the circular path, they naturally emit high-quality X-ray radiation.
Synchrotrons are large, costly and usually in high-demand by scientists, so Matthias Fuchs of the Max-Planck-Institute for Quantum Optics in Garching, Germany, and his colleagues have been working on another way to generate electrons.
Rather than using conventional magnets to guide and accelerate electrons, the team used a powerful laser beam and a small cell of hydrogen gas. They shot a brief, 37-femtosecond (10-15 seconds) pulse into the cell to blow the electrons off the hydrogen atom's nuclei. But electrical attraction causes the electrons to snap back towards the positive ions, so for a brief period after the pulse the electrons vibrate back and forth around the hydrogen atom's positive core, producing a wave. As they do so, a few electrons break loose and ride the crest of the electron wave. "Just like a surfer, the electrons can surf down these waves," Fuchs says.
The electrons then sail through a series of magnetic lenses, which feed them into a second series of magnets that cause them to wiggle back and forth — releasing low-energy 18-nanometre wavelength X-rays as they go.
Short pulse
Because the electric fields between the hydrogen ions and their electrons are so large, the electrons pick up speed much more rapidly than they would in a conventional accelerator. That means a machine the size of a building can be shrunk to the size of a tabletop. Well, almost. Fuchs says that including the laser, the accelerator takes up two fairly large tables. "We came up with the phrase 'banquet tabletop'," he says. The team's research has been published by Nature Physics1.
Nevertheless, "it is exciting", says Tom Katsouleas, dean of engineering at Duke University in Durham, North Carolina. Other groups had already shown lower-power radiation from similar systems, so it wasn't surprising, he adds. "I don't think anybody really doubted it could be done." "But they've actually shown that the beam quality can be fairly high," he says.
Because relatively few electrons are accelerated, the pulses are bright but short, so the 'tabletop' accelerator is unlikely to replace conventional synchrotrons any time soon. Still, Katsouleas says, there is no reason, in principle, why they could not be made into a workable X-ray source for use in universities.
References
1. Fuchs, M. et al. Nature Phys. advance online publication doi:10.1038/NPHYS1404 (2009).
[naturenews]
Published online 27 September 2009 | Nature | doi:10.1038/news.2009.954
News
Sex chromosomes linked to evolution of new species
Questions over conflict of the sexes remain.
By Natasha Gilbert
Experiments in stickleback fish have shown for the first time that the evolution of new sex chromosomes is the driving force behind the formation of a new vertebrate species.
Up until now, most evidence has shown that new species arise because they have adapted to new environments. But a study to be published by Nature1 found that the emergence of new sex chromosomes caused a population of threespine stickleback fish in the Japan Sea, to diverge from its Pacific Ocean–dwelling ancestor (Gasterosteus aculeatus) — creating a new species.
Jun Kitano, an evolutionary biologist at Tohoku University in Japan, and his team discovered that the Japan Sea stickleback fish had different sex chromosomes compared to their ancestors. The ancestral Y sex chromosome (which makes males) had fused with a non–sex chromosome to create a new sex chromosome in the Japan Sea stickleback fish.
The team also observed that the Japan Sea males exhibited more aggressive mating behaviours than their ancestral populations. Females from the ancestral population avoid mating with the Japan Sea fish due to their more aggressive behaviour. And in lab tests, the male progeny of the two populations were sterile.
The study found that the gene responsible for the aggressive mating behaviour of the Japan sea males was on the new Y chromosome. The new mating behaviours linked to the new sex chromosome stop the two populations from mating, making the Japan Sea population a new species.
"There is a gene on the new sex chromosome that causes differences in mating behaviour in the male stickleback. This behaviour leads to evolution of a new species of stickleback," says Catherine Peichel, a molecular biologist at the Fred Hutchinson Cancer Research Center in Seattle, Washington, and a member of the research team that published the study.
Battle of the sexes
Ole Seehausen, a fish ecologist and evolutionist at the Swiss Federal Institute of Aquatic Science and Technology in Dübendorf, says the study is "remarkable". "This is the first study that has shown a direct link between the evolution of sex chromosomes in vertebrates and the evolution of a new species," he says.
Peichel says that not much is known about what drives the evolution of new sex chromosomes. Scientists have hypothesized that conflict between the sexes could be behind this. If species carry genes that could be advantageous to males but detrimental to females, then natural selection will favour that these genes be located in the part of the genome that appears in males but not in females.
"A good place for them to be is right next to the gene that causes sex determination," says Peichel.
However the study has not yet answered whether conflict between the sexes drives the evolution of new sex chromosomes. "They do not prove that there is sexual conflict over the trait they study — that is that it is good for males but not females," Seehausen says.
References
1. Kitano, J. et al. Nature doi:10.1038/nature08441 (2009).
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