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qweff110
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Alaturat: 21 Iulie 2009
Mesaje: 5
Trimis: 21 Iulie 2009 , 08:33 | IP inregistrat Citat qweff110

HUMANS are not alone in struggling to stay slim. Some planets go through a "fat" stage that swells their waistlines temporarily, which possibly explains why some gas giants are unexpectedly large.

"Astronomers have power leveling  found a lot of planets whose sizes cannot be explained by standard theory," says Laurent Ibgui of Princeton University. The difference between predicted and measured widths of so-called "hot Jupiters" can be 30 per cent or more. 
 
Previously, astronomers assumed that, because cold gas takes up less volume than hot gas, hot Jupiters would shrink as they lost their initial heat.
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Now a computer simulation by Ibgui suggests this effect can be temporarily halted in hot Jupiters that begin life in highly elliptical orbits. These planets are alternately squeezed and stretched as they circle their stars, resulting in "tidal heating" that warms the gas inside the planet. This counteracts the cooling effect, inflating the planet - an effect that can last for a billion years or more. Eventually, though, the planet's orbit will become more circular, and the hot Jupiter resumes shrinking. Ibgui presented the research at an American Astronomical Society meeting in Pasadena, California, last week.
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The model doesn't quite explain the superpuffy appearance of all hot Jupiters, says Jonathan Fortney of the University of California, Santa Cruz. "It requires these planets to start their lives on very eccentric orbits, which is possible, but not currently the preferred scenario."

 

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lmaomao
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Alaturat: 23 Iulie 2009
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Trimis: 23 Iulie 2009 , 08:19 | IP inregistrat Citat lmaomao

The Einstein of the fish world may be the nine-spined stickleback, suggests new research that determined this common European fish possesses an unusually sophisticated capacity for learning not yet documented in any other animal, aside from humans.
The unassuming, small-headed fish proves tiny brains can yield "surprising cognitive abilities," according to project leader Jeremy Kendal, whose team discovered the stickleback can compare the behavior of other fish with its own experiences in order to make better choices.
This learning method, known as "hill-climbing," is necessary for cumulative culture and was thought to be unique to humans.
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"Cases such as nut-cracking in chimpanzees, or tool use in New Caledonian crows, are potentially consistent with such a strategy, but the strategy has yet to be shown unambiguously (in these other animals)," Kendal, a Durham University anthropologist, told Discovery News.
For the study, published in the journal Behavioral Ecology, he and his colleagues caught 270 nine-spined sticklebacks in Leicester, England. The fish were organized into experimental groups. These fish groups then took turns as either free swimmers in a tank with worm-yielding feeders at the end, or as "learners" in a transparent, partitioned-off area of the specially designed tank.
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One of the two feeders released more worms than the other. The fish quickly gravitated to this "rich feeder." When these fish then went into the observation semi-circle portion of the tank, the researchers swapped the feeders. The new free swimmers, as before, made a beeline for the feeder with a more plentiful worm reward.
When the observation fish group was released back into the part of the tank with the feeders, 75 percent were "clever" enough to know from watching the other sticklebacks that the feeders had been switched, so they didn't just rely upon their own experience with the feeders.
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Additional research conducted by the same team of scientists found that the likelihood of copying the behavior of another increased with the rate at which this other individual fed. The fish aren't therefore just mindlessly copying each other. They are instead "being selective about when and who they copy."
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Kendal thinks the nine-spined stickleback might have been "forced to learn" this rather complex strategy because the species is scrawnier than many other fish, with an anatomy that doesn't offer significant protection from predators. Instead of risking being eaten while searching for food, it benefits the fish to find out exactly where the best sources are at ahead of time and to go directly to them.
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"It is possible that, rather than evolve to become more sturdy, it is less costly for the nine-spines to evolve the capacity to exploit foraging information provided by observing others," he explained, mentioning that tougher three-spined sticklebacks don't seem to have such a brainy solution to foraging challenges.
Culum Brown, a University of Edinburgh researcher and editor of the book "Fish Cognition and Behavior," told Discovery News, the study "shows that fishes are using a mixture of their own knowledge and weighing it up against cultural information."
"In many ways," Brown said, "fish are just as smart as other animals."
While fish seem to exhibit frequent flashes of mental brilliance, the stickleback's hill-climbing strategy has yet to result in more human-like, high-tech capabilities, probably because fish habitats are so unstable.
"A massive constraint for the fish is that the environment can change rapidly, so information about a good foraging site can become redundant after a short time," Kendal said. "This resets the cumulative process and the fish have to start again acquiring new information."
"This means we might not expect any spectacular cumulative cultural evolution like seen in humans," he said, "but watch this space. We know so little and are constantly surprised about what they can do!"
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