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发表于 2014-2-26 12:08:27
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Part II:Speed
【Time 2】
Article 2
Making Virtual Humans Dance
CHICAGO, ILLINOIS—The motion capture technology that sent Na'vi prancing through Pandora with lifelike accuracy in the film Avatar has another use in the lab: creating fine-scale, highly personalized models of how a body moves. Computer scientist Nadia Magnenat Thalmann of the University of Geneva in Switzerland and colleagues have been working to design virtual replicas of athletes’ bodies—not just their general shape and movement, but also dynamics hidden within the joints that bear the strain. Their first test subjects: a group of professional ballerinas from the Grand Theater of Geneva. Due to the unusual stress on their joints as they dance, many ballerinas need hip replacement surgery in their early teens, says Thalmann, who described the ongoing modeling project here today at the annual meeting of AAAS, which publishes Science. The case study used MRI to generate a model of each dancer’s muscles, cartilage, and bone, slice by slice. Then, by adding data from a motion sensor suit (like the one in the photo above), the researchers watched how stress was distributed within the tissues (colored joint models, left) as she performed. The results have helped each dancer understand which movements put her at risk of long-term damage, Thalmann says, and predict the need for future surgery. This technology is still young, Thalmann points out, and the process of analyzing personalized data takes about a month. But she predicts that doctors will someday use the method to quickly model strain and injury in the clinic … even for those who don’t regularly subject their bodies to high kicks and splits.
Source:
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http://news.sciencemag.org/technology/2014/02/scienceshot-making-virtual-humans-dance
【Time 3】
Article 3
Acetaminophen use in pregnancy linked to kids’ slightly higher risk of ADHD
Women who take acetaminophen during pregnancy are more likely to have a child with attention-deficit/hyperactivity disorder than are women who don’t, according to an analysis of nearly 41,000 pairs of mothers and children in a Danish birth registry.
Researchers found that more than half of the women, who gave birth between 1996 and 2002, had used the pain reliever during pregnancy. Calls to the women when the children were 7 years old revealed that children whose moms used any acetaminophen during pregnancy were 37 percent more apt to be diagnosed with ADHD or a related disorder than children whose moms didn’t use the drug. If the women used it in all three trimesters, the apparent risk for offspring was 61 percent higher than for children whose mothers didn’t use the drug. Out of nearly 41,000 children, fewer than 1,000 were diagnosed with ADHD and related disorders.
The data establish an association and not cause and effect. But the researchers note that acetaminophen, also sold as Tylenol or Panadol, can cross the placental barrier and may affect hormones in a fetus.
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Source:
https://www.sciencenews.org/article/acetaminophen-use-pregnancy-linked-kids%E2%80%99-slightly-higher-risk-adhd
【Time 4】
Article 4
Cosmic light could close quantum-weirdness loophole
Distant quasars would decide whether quantum entanglement is an illusion.
Do you ever feel like the Universe is plotting against you? Strange as it may sound, physicists are planning to test whether a cosmic conspiracy could lie behind one of the weirdest phenomena in quantum physics, in which particles appear to influence each other, no matter how far they are separated. The experiment, proposed in a paper due to be published in Physical Review Letters, would use light from distant quasars to verify that this 'entanglement' is real. The test could also help cosmologists to distinguish between rival models of the early Universe.
Entanglement is a peculiarly quantum effect that links the states of separate objects, such as elementary particles, so that when one of the states is measured the properties of its twin are immediately affected. The notion that the particles influence each other faster than the speed of light famously galled Einstein, who argued instead that there could be some 'hidden variables' that influence the particles' behaviour in experiments, in line with classical physics.
Entanglement has been demonstrated in countless experiments starting in the 1970s, but a loophole could still invalidate the conclusion that the quantum explanation is correct: if hidden variables exist, then it is possible that they could influence the testing apparatus to give the illusion that correlations are more common than they are. This would require the history of the Universe to be pre-ordained to give scientists the illusion that they have complete freedom in how they set up their measurement, whereas in fact they do not.
In 2010, quantum physicist Anton Zeilinger of the University of Vienna and colleagues carried out a test that ruled out the possibility that hidden variables created during the experiment could have conspired with the detection apparatus. “But that left open the possibility that a conspiracy was set up further back in time, even just a few milliseconds before the experiment began,” says Andrew Friedman, a cosmologist at the Massachusetts Institute of Technology in Cambridge and a coauthor of the current paper.
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【Time 5】
Cosmic light
To minimize the risk of a conspiracy, both Zeilinger’s and Friedman’s teams are looking to the skies — in particular at light coming from energetic cosmic objects known as quasars. The plan is to set up a standard entanglement test in the laboratory. While it is running, the researchers will also measure light coming from two quasars on opposite sides of the sky. On the basis of, for instance, whether the light from the first quasar hits their telescope at an even or an odd nanosecond, they would then make a decision about which two properties of their first entangled particle to observe. They would similarly decide what measurements to make on the second entangled particle, on the basis of the arrival time of the light from the second quasar.
Quasars far enough apart would have formed in regions that have never been able to influence each other since the first fractions of a second after the Big Bang, some 13.8 billion years ago. If the results once again favour the quantum interpretation, the experiment would push the point in time at which any hidden-variable conspiracy could have occurred “far further back than it ever has been before”, says Zeilinger: to the beginning of the Universe itself.
Not everyone is convinced by the strategy, however. “It’s a cool idea to use light that originated a long time ago, in a galaxy far, far way, to make choices in your experiment,” says Richard Gill, who studies quantum statistics at the University of Leiden, the Netherlands. “The trouble is, they must detect this light signal using apparatus on the ground, so there’s still the opportunity for a conspiracy to arise in those detectors today.”
Friedman acknowledges Gill’s concern and says that it is up to them to minimize this possibility. Meanwhile, Zeilinger’s group is setting up the cosmic conspiracy test using telescopes in the Canary Islands, and the two teams hope to now collaborate.
As far as the outcome goes, Zeilinger is placing his bets on quantum weirdness: “I do not think we will see anything unexpected,” he says. Friedman agrees, but he adds, “You never know what you will see. Maybe quantum mechanics is wrong.”
If classical physics does prevail, Friedman notes, this could open the door to testing rivals models for the Universe’s history. The point at which the quantum correlations break down in the lab could be related to the duration of the period of exponential expansion thought to have occurred in the first instants of the Big Bang, known as cosmic inflation, says Friedman. “This quantum lab experiment could one day be used as a test of cosmology,” he says.
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Source:
http://www.nature.com/news/cosmic-light-could-close-quantum-weirdness-loophole-1.14771
【Time 6】
Article 5
A Mineral Mystery in the Driest Place on Earth
During his travels in South America in 1835, Charles Darwin came to the point where “the desert of Atacama commences, where nothing can exist.” Considered the driest place on Earth, the Atacama Desert receives less than 1 to 2 mm of rainfall each year. The only thing growing, it seems, is one of the world’s strangest mineral deposits (pictured). They appear as endless salt-encrusted desert basins, and their chemical composition makes them so unusual that some geologists say these minerals couldn’t exist in nature if the deposits weren’t right before their eyes. For instance, nitrate salts, like saltpeter, could be made by bacteria, except none have been detected in the desert. Other salts made from ions like dichromate are found nowhere other than the Atacama Desert. How these mineral deposits were made has puzzled geologists since Darwin, but a new study says that the minerals came from three separate sources. One source was sea spray from the Pacific Ocean, 50 kilometers to the east, bringing chlorine and sulfur, which landed in the desert and dried into salt crystals. Other minerals formed from thin air, as nitrogen in the atmosphere reacts with salts and dust, depositing nitrate minerals on the ground over time. And the last source, researchers report in an upcoming issue of Geology, was rain falling into the Andes Mountains 100 kilometers west of the Atacama, leaching material like dichromate ions into ground water flowing toward the desert; over millions of years, the mountains grew taller and the change in elevation forced more ground water toward the surface. At the same time, the parched desert climate was becoming increasingly drier. This aridity caused dissolved minerals in the ground water to precipitate into the vast mineral deposits seen today, creating a landscape unlike anywhere else in the world.
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Source:
http://news.sciencemag.org/chemistry/2014/02/scienceshot-mineral-mystery-driest-place-earth
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