- Megafauna Extinctions Not Entirely Humans’ Fault
- Genetically Modifying Songbirds to Study Human Brain Growth
- Superheavy Element 114 Finally Recreated
- Electric Fish Turn Down Charge for Energy Efficiency
- Quantum Entanglement Visible to the Naked Eye
- Dark Matter Hunters Construct a New Weapon
- Zoom In on Lagoon Nebula with Super-High-Res Image
Posted: 29 Sep 2009 10:37 AM PDT
BRISTOL, England — Studies that have mostly blamed the arrival of humans for die-offs among Australia's large mammals 50,000 years ago missed the role played by a changing climate, new research suggests.
Most assessments of Australian extinctions have used evidence gathered at sites that typically include fossils from only one narrow interval of time, Gilbert Price, a vertebrate paleontologist at the University of Queensland in St. Lucia, Australia, reported September 23 here at the meeting of the Society of Vertebrate Paleontology. But he and his colleagues have analyzed fossils of creatures both large and small from Darling Downs, a site in eastern Australia with a fossil record that extends from about 120,000 to about 55,000 years ago. In all, the team has tallied about 70 species that lived nearby at some point during that interval.
The data doesn't support a previously proposed human-only cause for Australian megafaunal extinctions, Price noted. From strata deposited about 120,000 years ago, the researchers recovered the remains of 15 species of large mammals. About 90,000 years ago, only eight species of large mammals lived there. By 55,000 years ago, still several millennia before humans arrived in the area, only four large mammal species remained.
That long-term drop in diversity also appeared among small creatures, and the types of species that disappeared suggest climate change played a role, Price said. Sediments deposited from 120,000 to 90,000 years ago contain the fossils of rodents, frogs and land snails as well as large mammals, suggesting that the surrounding area was a patchwork of woodlands, vine-choked thickets and open grasslands. By 55,000 years ago, however, many of the wet-loving and forest-adapted species had largely disappeared, signaling a transition to drier, more open conditions.
The new findings don't pin the blame for Australia's final spate of mammal extinctions on either climate change or human presence, Price cautioned. The long-term trend in species diversity at Darling Downs does hint, however, that climate change caused some species to die out. And the changes may have reduced the populations of other species enough that human arrival easily tipped them over the edge to extinction.
Image: Gilbert Price at Darling Downs in 2006. / Erika Fish, QUT Marketing & Communication
Posted: 29 Sep 2009 10:03 AM PDT
By genetically modifying the brains of songbirds for the first time, scientists may have a devised useful new tool for studying neurological growth and healing in humans.
"Songbirds have become a classic tool for studying vocal learning and neuron replacement. This will bring those two topics into the molecular age," said neuroscientist Fernando Nottebohm of Rockefeller University, author of a study September 28 in the Proceedings of the National Academy of Sciences.
Nottebohm's team successfully added fluorescent protein-producing genes to 23 zebra finches, a feat that — in the age of pet dogs clones and Alba the glow bunny — may not seem extraordinarily noteworthy at first glance. But unlike many other animals, including chickens and quail, songbirds have been remarkably hard to genetically modify. That's frustrating to scientists, who study the birds' ability to change their songs according to setting and experience.
That ability, known as vocal learning, is believed to rely on a version of the same neurological systems that eventually allowed a clever branch of the primate tree to acquire language and become human. It makes the birds an important model of human learning, language and neural development.
Nottebohm rose to fame during the 1990s, after finding that songbirds grew new brain cells in order to learn seasonal songs. That ran contrary to the conventional neurological truth of adults having a set number of brain cells. After being dismissed as fantasy, the ability has been found throughout the animal kingdom, including in humans.
All this has made songbirds as potentially important to understanding the growth of our brains as mice are to understanding our bodies. And now, just as it's possible to genetically modify mice, scientists might do the same in songbirds.
"When you talk about underlying mechanisms at the cellular level, you have to be able to manipulate genes. Otherwise, all your hypotheses are untestable," said Nottebohm. "It will open the door to a whole new generation of work on vocal learning that has not been possible."
Nottebohm's team injected 256 zebra finch embryos with viruses that traveled into the birds' genomes and inserted a gene that produced a fluorescent protein. When the birds hatched, cells containing the protein glowed.
The method is still in proof-of-principle stages, requiring between 10 and 20 injections per embryo. That repeated trauma could explain why just 23 of the embryos hatched, and only three passed on the genetic changes to their offspring.
"There's got to be a better way. We're delighted that we got it that far, but as we come to understand how this works, we would like to bring up the efficiency," said Nottebohm.
However, the importance of the technique is not in those early numbers, but the the possibility they represent, he said.
"We can test hypotheses that might explain how and why cells in the brain are replaced," said Nottebohm.
Images: 1. Scharff Lab 2. PNAS
Citation: "Transgenic songbirds: An opportunity to develop
Posted: 29 Sep 2009 09:48 AM PDT
By firing calcium isotopes into a plutonium target inside a particle accelerator, scientists at Lawrence Berkeley National Laboratory have finally confirmed the Russian discovery of the superheavy element 114.
It wasn't easy. It took more than a week of running the experiment to generate a measly two atoms of the stuff, which they reported in Physical Review Letters last week. It's basic science at the outer limits of matter.
"We're learning the limits of nuclei," said Ken Gregorich, a nuclear physicist at LBL. "How many protons can you pack into a nucleus before it falls apart?"
Uranium, which has 92 protons in its nucleus, is the heaviest element found in substantial quantities in nature. The first man-made "transuranic" elements like plutonium were discovered and synthesized during the 1940s in the run-up to the creation of nuclear weapons. Since then, it's gotten harder and harder to produce new elements, but scientists have kept at it. One reason is they hypothesized that certain isotopes of very heavy particles might exist in an "island of stability" that would allow them to stick around longer than the fractions of a second most synthetic elements last.
So, it was with great excitement that scientists received the news in early 1999 that the Joint Institute for Nuclear Research in Dubna appeared to have discovered Element 114 — and it lasted for whole seconds.
"It's fantastically important work," Neil Rowley of the Institute for Subatomic Research in Strasbourg, France told New Scientist in 1999.
Glenn Seaborg, Nobel Prize winner, adviser to presidents, and a big advocate of the island theory of superheavy elements, was even delivered the news of the Russian discovery on his death bed by an old friend.
"The term 'magic' was continually used — Seaborg and others spoke of a magic ridge, a magic mountain and a magic island of elements," wrote Oliver Sachs of the search for the island. "This vision came to haunt the imagination of physicists the world over. Whether or not it was scientifically important, it became psychologically imperative to reach, or at least to sight, this magic territory."
After decades of swimming through particle accelerator data, the island had been reached. It was tremendously big news.
Or so they thought.
As the years went by, the Russian team published a series of papers about Element 114, but other teams couldn't confirm their initial discovery of the extraordinarily long-lived particle. There were two reasons for this. One, the experimental apparatus required to check the findings were only available in a small number of labs around the world. Two, it appears the Russians were wrong.
"I think back in '99 they were learning how to do this and I think they had a random correlation of unrelated events that appeared to be Element 114," Gregorich said.
It's not that they didn't eventually discover Element 114. They did. It's just that their first observation, the most exciting one, turned out to be incorrect. In four separate publications from 2000 to 2004, they came up with better data, and those are the observations that Gregorich said his lab has confirmed.
And the island of stability? It is actually there, Gregorich said, but its effects are less pronounced than (at least) Seaborg hoped. The particular combinations of protons and neutrons do yield longer lasting elements, just not … magic ones.
"Our results and the Dubna results show that there is some stability there," Gregorich said. "If we didn't have extra stability due to the shell effects, these things would decay faster than we could ever detect them with lifetimes on the order of 10-20 seconds rather than 10-1 seconds."
The search, though, for a more perfect superheavy element does go on.
"There are still predictions that if you could use more neutron-rich projectiles, if you could produce these elements but with more neutrons, some of them would be pretty long lived," he said.
Unfortunately, the particle accelerators in operation and currently planned won't reach the power necessary to get to create the theoretically most stable elements.
"The present and next generation of radioactive beam machines don't have high enough beam intensities," Gregorich said. "The technology doesn't exist today but it might in another 20 or 30 years."
Image: The Berkeley Gas-filled Separator, the detector used in the experiment, in situ.
Posted: 28 Sep 2009 05:00 PM PDT
Fish that use electric fields to sense their environments dim their signals to save energy during the day when they are resting.
Sternopygus macrurus, a South American river fish, is a natural practitioner of energy efficiency. It can reshape the charged-molecule channels in its electricity-producing cells to tone down its electrical signature within a matter of minutes.
"This is a really expensive signal to produce. The fish is using up a lot of its energy budget," said neurobiologist Michael Markham at the University of Texas at Austin, lead author of a paper in PLoS Biology on the fish. "These animals are saving energy by reducing the strength of the signal when they are not active."
Thousands of fish and other oceanic creatures use electrical fields to help them perceive their environments. The most famous is the electric eel, which a colleague of Markham's termed "a frog with a cattle prod attached," but most animals use the electrical signals in more subtle ways.
The fish's standard electrical signal runs at 100 hertz; if you turn the electrical signal into sound, it sounds like a high whine. In laboratory experiments, the fish can detect tiny bugs half a centimeter wide and easily navigate obstacles by detecting the changes the objects cause in the electrical field.
All fish generate electricity with a specialized type of cell called an electrocyte. These cells can generate current by manipulating the amount of charged sodium and potassium ions that they allow to flow into and out of themselves. An electrical current propagates on the membrane of the cell as a result. Thousands of cells combine to generate the 5 millivolts per centimeter electrical field the fish uses. By using fewer sodium channels, the signal gets dimmed and energy is conserved.
"The wave form of the electric signal changes and at the level of the individual cell, it is changing its discharge," Markham said. "This is the first time in a vertebrate animal that you can show such a clear connection between an animal's behavior and the changes at the molecular level."
For Markham, the system is interesting because the ways cells reshape their membranes — scientists call the process ion channel trafficking — are very similar to the ones that our hearts and nervous systems use.
The same molecular machinery that drives our nervous system, muscles and heart has evolved into an organ just to produce electricity, he said. The specialized organ, then, acts as a kind of biological laboratory for evolutionary experiments with electricity production.
"If there is a slight mutation in the ion channels in your heart, that's very likely to be a fatal mutation," Markham said. "The electric organ from an evolutionary standpoint is a much more forgiving place for experimentation."
In the future, they hope to use their research on ion channels to better understand the kinds of electrical malfunctions that cause disorders like epilepsy.
"There's a kind of gee whiz interest factor to working with these fish, but obviously, we're pursuing a bigger agenda," Markham said.
Posted: 28 Sep 2009 02:41 PM PDT
By linking the electrical currents of two superconductors large enough to be seen with the naked eye, researchers have extended the domain of observable quantum effects. Billions of flowing electrons in the superconductors can collectively exhibit a weird quantum property called entanglement, usually confined to the realm of tiny particles, scientists report in the September 24 Nature.
Entanglement is one of the strangest consequences of quantum mechanics. After interacting in a certain way, objects become mysteriously linked, or entangled, so that what happens to one seems to affect the fate of the other. For the most part, researchers have only found signs of entanglement between tiny particles, such as ions, atoms and photons.
John Martinis and colleagues at the University of California, Santa Barbara looked for entanglement between two superconductors, each less than a millimeter across. These superconducting circuits, made of aluminum, were separated by a few millimeters on an electronic chip. At low temperatures, electrons in the superconductors flow collectively, unfettered by resistance.
Despite each superconductor's relatively large size, the electrons within move together in a naturally coherent way. "There are very few moving parts, so to speak," Girvin says, which helped the scientists spot evidence of entanglement. "It's a general fact that the larger an object is, the more classical it is in its behavior, and the more difficult it is to see quantum mechanical effects."
In the new study, researchers used a microwave pulse to attempt to entangle the electrical currents of the two superconductors. If the currents were quantum-mechanically linked, one current would flow clockwise at the time of measurement (assigned a value of 0), while the other would flow counterclockwise when measured (assigned a value of 1), Martinis says. On the other hand, the currents' directions would be completely independent of each other if everyday, classical physics were at work.
After attempting to entangle the superconducting circuits, Martinis and his team measured the directions of the currents 34.1 million times. When one current flowed clockwise (measured as a 0), the team found, the other flowed counterclockwise (measured as a 1) with very high probability. So the two were linked in a way that only quantum mechanics could explain.
"It has to be in this weird quantum state for you to get those particular probabilities that we measure," Martinis says. "The percentages of those different things are not something that you can classically predict."
Finding entanglement between superconductors is "a fairly important milestone," comments Anthony Leggett of the University of Illinois at Urbana-Champaign. The new study "does seem to be rather unambiguous evidence for entanglement."
Such entangled superconductors might be used as a component in a powerful quantum computer, Leggett says. "People are very interested in the possibility of building a quantum computer," and these kinds of systems may be quite good for that, he says.
Martinis says that the technology for building advanced electrical circuits may be used to build quantum circuits, too. "The hope is that since we know how to put together integrated circuits in complex ways, that maybe we can make very complex quantum circuits in the same way," he says.
He cautions, though, that a good quantum computer is a long way off. Researchers still need to find a way to make entangled superconducting circuits last longer. And a good quantum computer would need more than two circuits. Martinis says his group will try to entangle three and four such circuits next.
In addition to providing technological advances, the new results add to the debate over where to draw the line between quantum mechanics and the everyday physics that governs large-scale phenomena. Researchers want to know how far quantum weirdness can go.
"It's interesting to test quantum mechanics on a large scale," Girvin says. "Do things look classical on large scales because there's something wrong with quantum mechanics? Personally, I think that's wrong, but one never knows."
Image: Erik Lucero
Posted: 28 Sep 2009 01:54 PM PDT
That dark matter has never been found is no deterrent to the physicists who are looking for it.
"Even if we don't know what dark matter is, we know how it must act," said Eduardo Abancens, a physicist at Spain's University of Zaragoza and designer of a prototype dark matter detector.
According to physicists, only around five percent of what makes up the universe can presently be detected. The existence of dark matter is inferred from the behavior of faraway galaxies, which move in ways that can only be explained by a gravitational pull caused by more mass than can be seen. They estimate dark matter represents around 20 percent of the universe, with the other 75 percent made up of dark energy, a repulsive force that is causing the universe to expand at an ever-quickening pace.
At the heart of Abancens' team's detector, which is called a scintillating bolometer and resembles a prop from The Golden Compass, is a crystal so pure it can conduct the energy ostensibly generated when a particle of dark matter strikes the nucleus of one of its atoms.
To prevent interference by cosmic rays, the bolometer is sheathed in lead and kept underground, under half a mile of rock. It's also frozen to near-absolute zero, the temperature at which all motion stops. At the edge of absolute zero, it's possible to measure expected changes of a few millionths of a degree Fahrenheit.
Researchers like Abancens call this "a high heat signal."
As described in a paper published in the August Optical Materials and released online Friday, the bolometer is currently able to distinguish between the vibrations produced by trembling nuclei and spinning electrons. Abancens said it could be operational in five years.
But in order for the bolometer to work reliably, it needs to become even more sensitive, and maintain that sensitivity as it's scaled up from the 46-gram prototype to a half-ton working model, said Rick Gaitskell, a Brown University physicist who was not involved in the research.
At near-absolute zero, conducting research is "quite challenging," said Gaitskell, who spent a decade trying to make detection systems work at that temperature.
"Now we're using using liquid xenon. It's relatively warm, only minus 150 degrees Fahrenheit," he said. "You can nearly get to that in an industrial-strength refrigerator."
Citation: "A BGO scintillating bolometer as dark matter detector prototype." By N. Coron, E. García, J. Gironnet, J. Leblanc, P. de Marcillac, M. Martínez, Y. Ortigoza, A. Ortiz de Solórzano, C. Pobes, J. Puimedón, T. Redon, M.L. Sarsa, L. Torres and J.A. Villar. Optical Materials, Vol. 31 Issue 10, August 2009.
Image: The blue glow comes from the photographer's flash.
Posted: 28 Sep 2009 10:14 AM PDT
A huge new image of the Lagoon Nebula, covering an area of the sky eight times larger than the full moon, has been released by the European Southern Observatory.
Located four to five thousand light-years away in the direction of Sagittarius, the nebula is a cloud of dust and gas about 100 light-years across. Bright, star-forming clusters can be seen scattered throughout the reddish nebula, which acquires its color from small particles that scatter white light.
The image is the third in a "trilogy" plotted and executed by the ESO for the International Year of Astronomy 2009. The previous GigaGalazy Zoom images showcased the best the unaided human eye and an amateur telescope could do. The latest photo steps up to the pro level by using the 67-million-pixel Wide Field Imager attached to the 2.2-meter telescope at the La Silla Observatory in the Atacama desert of Chile.
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