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发表于 2013-12-10 23:16:41
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Part II:Speed
【Time 2】
Article 2
Massive 'Cells' Seen on Sun
Large flows of material that circulate heat from the sun’s interior to its surface, theorized since the late 1960s but never seen directly, have finally been spotted. Researchers have long known of smaller flows called granules (which last a few minutes and are typically about 1000 kilometers across) and supergranules (which last about 1 day and are usually about 30,000 km across). The new swirls, which roil the outermost 30% of the sun’s interior, are several hundreds of thousands of kilometers across and persist for several months, the researchers report online today in Science. The team analyzed space-based observations of the sun taken every 45 seconds for several years. After removing the effects of solar rotation and accounting for the angle of view of areas not facing directly toward Earth, the researchers could discern the so-called giant cell flow patterns (material moving east is depicted in red, that moving toward the west in blue), which cause supergranules to slowly drift across the surface of the sun. Flow speeds within the giant cells, akin to the convection that carries hot water from the bottom of a heated pan to the surface, are only a few meters per second, the researchers estimate. But the overall effects of these flows (such as the long, jet stream-like red swath in the sun’s northern hemisphere) are important. Among other things, giant cell circulation helps transport energy from the sun’s polar regions to its equator, where material rotates around the sun about 10 days faster than it does near the poles. The flows also substantially influence the structure and evolution of the sun’s magnetic field, the researchers suspect. Active regions on the solar surface, often the sources of solar flares, may form in areas where flows converge, causing magnetic fields to become concentrated.
字数[297]
Source:
http://news.sciencemag.org/physics/2013/12/scienceshot-massive-cells-seen-sun
【Time 3】
Article 3
How to Green Your Firing Range
Firing ranges host some of the planet’s most heavily contaminated soils. Toxic lead and copper from spent bullets can leach into the earth, threatening ground water, killing microbes, and poisoning plants. Cleaning this soil is often too costly for the operators of military and private ranges. Now, Korean scientists have created a natural mixture that sops up nearly all the metals: pulverized oyster shells and fly ash, the sooty particles spewed by combustion. Landfills in Korea accumulate more than 250,000 tons of oyster shells each year, while coal-fired power plants churn out just as much fly ash. Combining the two waste products creates a concoction rich in minerals that shackle metal ions within tight molecular bonds, the team reports this month in Environmental Geochemistry and Health. By mixing different ratios of the ingredients with grossly contaminated firing-range soil—holding nearly seven times the amount of lead deemed dangerous by the U.S. Environmental Protection Agency—the researchers identified a unique blend that locked up 98% of leachable lead contamination and 96% of the copper. Other soil-scouring techniques exist, but the shells-and-ashes approach is far cheaper and more sustainable, the scientists claim.
字数[190]
Source:
http://news.sciencemag.org/environment/2013/12/scienceshot-how-green-your-firing-range
【Time 4】
Article 4
Predators May Use a Bit of the Old Razzle Dazzle to Snag Prey
In 1917, British artist Norman Wilkinson experienced a eureka moment while serving in the Royal Naval Volunteer Reserve. Throughout the month of April, German U-boats had been mercilessly torpedoing British ships, sending around eight of those vessels per day into the watery abyss. Hiding a ship traveling on the open ocean from plain sight was impossible, Wilkinson knew, but a bit of artistic trickery may be able to muddle the Germans’ ability to accurately judge the exact location of that ship, he realized.
From that idea, Wilkinson devised a type of camouflage called “razzle dazzle” (its slightly more serious name is dazzle camouflage). The technique consists of squashing together contrasting geometric patterns, shapes and colors to create a pattern of optics that would confuse enemies by distorting the object’s dimensions and boundaries. All in all, more than 2,000 ships received such a makeover, although the scheme’s effectiveness seemed to produce mixed results.
By World War II, razzle dazzle had largely fallen out of favor, but as it turns out, this technique lives on in the natural world. High contrast patterns–nature’s equivalent to dazzle camouflage–are used by animals ranging from snakes to zebra to fish. Like those hidden World War I ships, many creatures seem to use dazzle patterns to conceal themselves from predators. Until now, however, researchers hadn’t considered the flipside of this relationship: could predators use razzle dazzle to sneak up on prey as they mounted an attack?
To investigate this possibility, biologist Roger Santer of Aberystwyth University in the U.K. turned to locusts. These insects are particularly well suited for vision studies due to something called a single lobula giant movement detector neuron, a unique cell that specializes in detecting looming objects (think of a car speeding towards you, or a hand reaching for your face). Researchers think this neuron works by measuring the shape and movement of patterns of light and dark across the eye. Whatever the mechanism, as looming objects approach a locust, its detector neuron fires away, alerting the insect to imminent potential danger and triggering it to flee.
字数[346]
【Time 5】
To see how the locusts responded to dazzle camouflage, Santer created an array of visual patterns using a graphics software. He situated the locusts just in front of the computer monitor, and then projected a simulated approach of those objects from about 10 meters away to about 0.07 meters from the cowering insects. The objects varied in contrast: black, grey or white on a grey background. Around 20 locusts took part in the experiment, and Santer measured their cellular reactions to the various shapes through copper wires inserted into the locusts’ neck.
The locusts’ neurological responses to the looming objects depended on which patterns they saw, Santer reports in Biology Letters. Squares with both a darker-than-background top and bottom half elicited the strongest panic response, followed by squares with a dark upper half, but a bottom half that was the same color as the background. Squares that had an upper half that was dark but a bottom half that was bright (in other words, the razzle dazzle ones) produced a significantly weaker panic response, as did squares that were brighter than the background. Finally, squares that were the same color as the background produced no response at all.
These results are interesting in that they correlate with similar dazzle tests performed on humans, who also had trouble quickly registering dazzle patterns. However, at this point, whether or not locust predators actually use dazzle to catch their unsuspecting insect prey remains a matter of speculation. Though lab tests confirm this strategy might work, Santer did not investigate whether or not a dazzle dance of death is carried out in the real world.
Hypothetically speaking, dazzle camouflage, Santer concludes, would help a predator but would not be the most effective way of snagging a locust lunch. Instead, classic camouflage–blending in with the background rather than creating an optical illusion–seems to be the most effective means of tricking would-be prey. However, in the case that other selection pressures favor high-contrast patterns (such as if females of a predator species prefer bold stripes in males), Santer thinks that predators could indeed evolve to give ‘em the old razzle dazzle.
字数[357]
Source:
http://blogs.smithsonianmag.com/science/2013/12/predators-may-use-a-bit-of-the-old-razzle-dazzle-to-snag-prey/
【Time 6】
Article 5
Mercury shrinking more than thought
Latest views of the planet settle a decades-old argument about its evolution.
The planet closest to the Sun has shrivelled much more over its lifetime than previously thought, scientists have found.
Studies of Mercury show that it has shrunk by about 11 kilometres across since the Solar System's fiery birth 4.5 billion years ago. As the planet cooled and contracted, it became scarred with long curved ridges similar to the wrinkles on a rotting apple.
A new census of these ridges, called lobate scarps, has found more of them, with steeper faces, than ever before. The discovery suggests that Mercury shrank by far more than the previous estimate of 2-3 kilometres, says Paul Byrne, a planetary scientist at the Carnegie Institution for Science in Washington DC. He presented the results today at a meeting of the American Geophysical Union in San Francisco, California.
The finding helps explain how Mercury's huge metallic core cooled off over time. It may also finally reconcile theoretical scientists, who had predicted a lot of shrinkage, with observers who had not found evidence of that — until now. “We are resolving a four-decades-old conflict here,” Byrne told the meeting.
Planetary scientists have been arguing over Mercury's lobate scarps ever since the Mariner 10 spacecraft flew past the planet three times in 1974-75. Researchers can use measurements of the length and height of the scarps to calculate how much planetary shrinkage they represent.
That shrinkage is a product of Mercury's odd composition — “like a core floating through space with a thin outer blanket,” says Byrne. Most of the planet is made of that large core, and so it would have cooled rapidly as heat rushed toward its surface. Modelling studies have long suggested that the planet should have shrunk by 10-20 kilometres over its lifetime, compared to the 2-3 kilometres estimated from Mariner 10 data1.
The latest estimates come from NASA’s MESSENGER probe, which photographs and measures Mercury's topography. Last year, Italian scientists used MESSENGER data covering one-fifth of the planet to show that its shrinkage was probably greater than the Mariner 10 estimates2.
The latest work, covering the entire planet, revealed many lobate scarps with sharp vertical relief, Byrne said. It also uncovered details on another kind of surface feature that may be related to shrinkage. These ‘wrinkle ridges’ are less pronounced than the lobate scarps but may also have formed during contraction. Combined, the data on the lobate scarps and the wrinkle ridges suggest that Mercury's diameter has shrunk by 11.4 kilometres, Byrne said. Even leaving out the wrinkle ridges gives 10.2 kilometres of contraction.
Those numbers are plausible to at least one planetary scientist who studied Mercury’s shrinkage using Mariner 10 data in the 1970s. Jay Melosh, a planetary geologist at Purdue University in West Lafayette, Indiana, suspects that even more lobate scarps may be lurking out there. “Many of these things may still be hiding,” he says. “As far as I'm concerned, this may be an underestimate of the amount of shrinkage.”
字数[486]
Source:
http://www.nature.com/news/mercury-shrinking-more-than-thought-1.14331
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