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【计时一】
Intelligence Is in the Genes, but Where? Most Genes Thought to Be Linked to Intelligence Probably Have No Bearing On IQ
ScienceDaily (Oct. 2, 2012) — You can thank your parents for your smarts -- or at least some of them. Psychologists have long known that intelligence, like most other traits, is partly genetic. But a new study led by psychological scientist Christopher Chabris of Union College reveals the surprising fact that most of the specific genes long thought to be linked to intelligence probably have no bearing on one's IQ. And it may be some time before researchers can identify intelligence's specific genetic roots.
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Chabris and David Laibson, a Harvard economist, led an international team of researchers that analyzed a dozen genes using large data sets that included both intelligence testing and genetic data.
In nearly every case, the researchers found that intelligence could not be linked to the specific genes that were tested. The results are published online in Psychological Science, a journal of the Association for Psychological Science.
"In all of our tests we only found one gene that appeared to be associated with intelligence, and it was a very small effect. This does not mean intelligence does not have a genetic component. It means it's a lot harder to find the particular genes, or the particular genetic variants, that influence the differences in intelligence," said Chabris.
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【计时二】
It had long been believed, on the basis of studies of identical and fraternal twins, that intelligence was a heritable trait. The new research affirms that conclusion. But older studies that picked out specific genes had flaws, Chabris said, primarily because of technological limits that prevented researchers from probing more than a few locations in the human genome to find genes that affected intelligence.
"We want to emphasize that we are not saying the people who did earlier research in this area were foolish or wrong," Chabris said. "They were using the best technology and information they had available. At the time, it was believed that individual genes would have a much larger effect -- they were expecting to find genes that might each account for several IQ points."
Chabris said additional research is needed to determine the exact role genes play in intelligence.
"As is the case with other traits, like height, there are probably thousands of genes and their variants that are associated with intelligence," he said. "And there may be other genetic effects beyond the single gene effects. There could be interactions among genes, or interactions between genes and the environment. Our results show that the way researchers have been looking for genes that may be related to intelligence -- the candidate gene method -- is fairly likely to result in false positives, so other methods should be used."
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【计时三】
Case of Missing Quasar Gas Clouds Now Solved
ScienceDaily (Oct. 2, 2012) — The case of the missing quasar gas clouds has been solved by a worldwide research team led by Penn State astronomers Nurten Filiz Ak and Niel Brandt. The discovery was announced Oct. 1 in a paper published in The Astrophysical Journal, which describes 19 distant quasars whose giant clouds of gas seem to have disappeared in just a few years.
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"We know that many quasars have structures of fast-moving gas caught up in 'quasar winds,' and now we know that those structures can regularly disappear from view," said Filiz Ak, a graduate student in the Department of Astronomy and Astrophysics at Penn State and lead author of the paper. "But why is this happening?"
Quasars are powered by gas falling into supermassive black holes at the centers of galaxies. As the gas falls into the black hole, it heats up and gives off light. The gravitational force from the black hole is so strong, and is pulling so much gas, that the hot gas glows brighter than the entire surrounding galaxy. But with so much going on in such a small space, some of the gas is not able to find its way into the black hole. Much of it instead escapes, carried along by strong winds blowing out from the center of the quasar.
"These winds blow at thousands of miles per second, far faster than any winds we see on Earth," said Niel Brandt, a Distinguished Professor of Astronomy and Astrophysics at Penn State and Filiz Ak's doctoral adviser. "The winds are important because we know that they play an important role in regulating the quasar's central black hole, as well as star formation in the surrounding galaxy."
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【计时四】
Many quasars show evidence of these winds in their spectra -- measurements of the amount of light that the quasar gives off at different wavelengths. Just outside the center of the quasar are clouds of hot gas flowing away from the central black hole. As light from deeper in the quasar passes through these clouds on its way to Earth, some of the light gets absorbed at particular wavelengths corresponding to the elements in the clouds.
As gas clouds are accelerated to high speeds by the quasar, the Doppler effect spreads the absorption over a broad range of wavelengths, leading to a wide valley visible in the spectrum. The width of this "broad absorption line" (BAL) measures the speed of the quasar's wind. Quasars whose spectra show such broad absorption lines are known as "BAL quasars."
But the hearts of quasars are chaotic, messy places. Quasar winds blow at thousands of miles per second, and the disk around the central black hole is rotating at speeds that approach the speed of light. All this action adds up to an environment that can change quickly.
Previous studies had found a few examples of quasars whose broad absorption lines seemed to have disappeared between one observation and the next. But these quasars had been found one at a time, and largely by chance -- no one had ever done a systematic search for them until 1998, when the Sloan Digital Sky Survey (SDSS) undertook the challenge, in 1998, of regularly measuring the spectra of hundreds of quasars during an effort spanning several years.
Over the past three years, as part of SDSS-III's Baryon Oscillation Spectroscopic Survey (BOSS), the researchers specifically have been seeking out repeated spectra of BAL quasars through a program proposed by Brandt and his colleagues.
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【计时五】
Their persistence paid off -- the research team gathered a sample of 582 BAL quasars, each of which had repeat observations over a period of between one and nine years -- a sample about 20 times larger than any that previously had been assembled. The team then began to search for changes, and found that, in 19 of the quasars, the broad absorption lines had disappeared.
There are several possible explanations for the disappearance of the gas clouds, but the simplest is that, in these quasars, gas clouds that previously had been detected are now "gone with the wind" -- blown out of the line-of-sight between us and the quasar by the rotation of the quasar's disk and its wind. Because the sample of quasars is so large, and had been gathered in such a systematic manner, the team is able to go beyond simply identifying disappearing gas clouds. "We can quantify this phenomenon," Ak said.
Finding 19 such quasars out of 582 total indicates that about three percent of quasars show disappearing gas clouds over a three-year span, which in turn suggests that a typical quasar cloud spends about a century along our line of sight. "It is fascinating to be able to document these relatively rapid changes that actually occurred billions of years ago, at a time before the Sun was formed," remarked team member Donald Schneider, distinguished Professor of Astronomy and Astrophysics at Penn State and the SDSS-III Survey Coordinator.
Now, as other astronomers come up with models of quasar winds, their models will need to explain this 100-year timescale. As theorists begin to consider the results, and the team continues to analyze its sample of quasars, more results are expected soon. "This research is really exciting for me," Filiz Ak said. "I'm sitting at my desk, discovering the nature of the most powerful winds in the Universe."
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【越障】
Thanks for the Transparent Memories: Progress in Quest for Reliable, Flexible Computer Memory for Transparent Electronics
ScienceDaily (Oct. 2, 2012) — Very few discoveries happen in an instant. Few discoverers go, "Aha!" More often, the truth reveals itself to scientists the same way a statue comes to light as a sculptor chips away.
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This happens even when the work of art is on the nanoscale, where individual things make a strand of hair look like a redwood by comparison.
More than four years ago, a collection of students, postdoctoral researchers and professors at Rice University found themselves chiseling down into a mystery involving two of the most basic, common elements on Earth: carbon and silicon oxide.
The group led by chemist James Tour came to a discovery of note: that it was possible to make bits of computer memory from those elements, but make them much smaller and perhaps better than anything on the market even today.
From that first revelation in 2008 to now, Tour and his team have steadily advanced the science of two-terminal memory devices, which he fully expects will become ubiquitous in the not-too-distant future.
The latest dispatch is a paper in the journal Nature Communications that describes transparent, non-volatile, heat- and radiation-resistant memory chips created in Tour's lab from those same basic elements, silicon and carbon. But a lot has happened since 2008, and these devices bear only a passing resemblance to the original memory unit.
In the new work, Tour and his co-authors detail their success at making memory chips from silicon oxide sandwiched between electrodes of graphene, the single-atom-thick form of carbon.
Even better, they were able to put those test chips onto flexible pieces of plastic, leading to paper-thin, see-through memories they hope can be manufactured with extraordinarily large capacities at a reasonable price. Think about what that can do for heads-up windshields or displays with embedded electronics, or even flexible, transparent cellphones.
"The interest is starting to climb," said Tour, Rice's Rice's T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science. "We're working with several companies that are interested either in getting their chips to do this kind of switching or in the possibility of making radiation-hard devices out of this."
In fact, samples of the chips have climbed all the way to the International Space Station (ISS), where memories created and programmed at Rice are being evaluated for their ability to withstand radiation in a harsh environment.
"Now, we've seen a couple of DARPA announcements asking for proposals for devices based on silicon oxide, the very thing we've shown. So there are other people seeing the feasibility of this approach," Tour said.
It wasn't always so, even if silicon oxide "is the most studied material in humankind," he said.
"Labs in the '60s and '70s that saw the switching effect didn't have the tools to understand what they were looking at," he said. "They didn't know how to exploit it; they called it a soft breakdown in silicon. To them, it was something bad."
In the original work at Rice, researchers put strips of graphite, the bulk form of carbon best known as pencil lead, across a silicon oxide substrate and noticed that applying strong voltage would break the carbon; lower voltages would repeatedly heal and re-break the circuit. They recognized a break could be a "0″ and a healed circuit a "1." That's a switch, the most basic memory state.
Manufacturers who have been able to fit millions of such switches on small devices in the likes of flash memory now find themselves bumping against the physical limits of their current architectures, which require three wires -- or terminals -- to control and read each bit.
But the Rice unit, requiring only two terminals, made it far less complicated. It meant arrays of two-terminal memory could be stacked in three-dimensional configurations that would vastly increase the amount of information a chip could hold.
【667】
【剩余部分】
And best of all, the mechanism that made it possible turned out not to be in the graphite, but the silicon oxide. In the breakthrough 2010 paper that followed the 2008 discovery, the researchers led by then-graduate student Jun Yao found that a strong jolt of voltage through a piece of silicon oxide stripped oxygen atoms from a channel only 5 nanometers wide, turning it into pure silicon. Lower voltages would break the channel or reconnect it, repeatedly, thousands of times.
"Jun was the first to recognize what he was seeing," Tour said. "Nobody believed him, though (Rice physicist) Doug Natelson said, 'You know, it's not out of the realm of possibility.' The people on the graphitic memory project were not at all excited about him saying this and they argued with Jun tooth and nail for a couple of years."
Yao struggled to convince his lab partners the switching effect wasn't due to the breaking graphite but to the underlying crystalline silicon. "Jun quietly continued his work and stacked up evidence, eventually building a working device with no graphite," Tour said. Still, he recalled, Yao's colleagues suspected that carbon in the system skewed the results. So he demonstrated another device with no possible exposure to carbon at all.
Yao's revelation became the basis for the next-generation memories now being designed in Tour's lab, where silicon oxides sandwiched between graphene layers are being attached to plastic sheets. There's not a speck of metal in the entire unit (with the exception of leads attached to the graphene electrodes). And the eye can see right through it.
"Now we're making these memories with about an 80 percent yield of working devices, which is pretty good for a non-industrial lab," Tour said. "When you get these ideas into industries' hands, they really sharpen it up."
The idea of transparency came later. "Silicon oxide is basically the same material as glass, so it should be transparent," Tour said. Graphene sheets, single-atom-thick carbon honeycombs, are almost completely transparent, too, and tests detailed in the new paper showed their ability to function as crossbar electrodes, a checkerboard array half above and half below the silicon oxide that creates a circuit where the lines intersect.
The marriage of silicon and graphene would extend the long-recognized utility of the first and prove once and for all the value of the second, long touted as a wonder material looking for a reason to be.
"It was a very rewarding experience," said Yao, now a postdoctoral researcher at Harvard, of his work at Rice. "I feel grateful that I stumbled on this, had the support of my advisers and persisted."
By good fortune, Yao was the rare graduate student with three advisers. As confusing as that may have seemed at the start of his Rice career, it was luck those advisers were digital systems expert Lin Zhong and condensed matter physicist Natelson, both rising stars in their fields, and Tour, a renowned chemist.
Each made important contributions to the project as it progressed. "Doug had very acute intuition about the underlying mechanism, and we constantly turned to Lin for his advice on the electronic architecture," Yao said.
Getting his story on Page 1 of the New York Times was enough of a thrill, but another was ahead as NASA decided to include samples of his chip in an experimental package bound for the space station. The day of Yao's planned departure for his postdoctoral job in Cambridge, Aug. 24, 2011, was to be the best of all as the HIMassSEE project lifted off from Central Asia aboard a cargo flight to the ISS. Minutes later, the unmanned craft crashed in Siberia.
Nearly a year later, a new set of chips made it to the ISS, where they will stay for two years to test their ability to hold a pattern when exposed to radiation in space.
In the meantime, Yao passed responsibility for the project to Jian Lin, a co-author of the new paper who joined the Tour and Natelson labs in 2011 as a postdoctoral researcher. Lin built the latest iterations of silicon oxide memories using crossbar graphene electrodes.
"Our lab members are excellent at synthesizing materials and I'm good at fabrication of devices for various applications, so we work together well," said Lin, whose primary interest is in the application of nanomaterials. "This group is a win-win for me."
Labs at other institutions have picked up the thread, carrying out their own experiments on silicon oxide memory. "The switching mechanism has pretty much been investigated," Lin said. "But from engineering or application perspectives, there are a lot of things that can be done."
So here silicon memory stands, a toddler full of promise. Researchers at Rice and elsewhere are working to increase silicon memory's capacity and improve its reliability while electronics manufacturers think hard about how to make it in bulk and put it into products.
Tour realizes impatience for scientific progress is a function of hurried times and not a failure of the process, but he counsels against frustration. "It's a very interesting system that has been slow to develop," he said, "as we've been working to understand the fundamental switching mechanism," a task largely accomplished by Yao and his Rice advisers in a paper published earlier this year. "This is now transitioning slowly into an applied system that could well be taken up as a future memory system.
"It is a good example of basic research," he said. "Now, others have to be able to look forward from the science and say, 'You know, there's a path to a product here.'"
Co-authors of the Nature Communications paper are Rice graduate students Yanhua Dai, Gedeng Ruan, Zheng Yan and Lei Li. Zhong is an associate professor of electrical and computer engineering. Natelson is a professor of physics and astronomy and of electrical and computer engineering.
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发表于 2012-10-3 10:47:53
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eople are working on new computer memory chips made from silicon and carbon.
