【每日阅读训练第二期——速度越障5系列】【5-16】

xinnono

North Star May Be Wasting Away
by Kate McAlpine on 27 January 2012, 1:02 PM
摘自http://news.sciencemag.org/sciencenow/2012/01/north-star-may-be-wasting-away.html

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The North Star, a celestial beacon to navigators for centuries, may be slowly shrinking, according to a new analysis of more than 160 years of observations. The data suggest that the familiar fixture in the northern sky is shedding an Earth's mass worth of gas each year. Some researchers caution, however, that the conclusion depends on certain assumptions about exactly where the star is in its several-billion-year life cycle.
Also known as Polaris, the North Star always sits over the North Pole because it is aligned with Earth's axis. Find it in the night sky, at the end of the Little Dipper's handle, and you don't need a compass to orient yourself. To weigh Polaris, astrophysicist Hilding Neilson of the University of Bonn in Germany and colleagues essentially took its pulse. The star grows dimmer and brighter over a roughly 4-day cycle, and the team studied variation in the length of that cycle. Like all stars, Polaris is made of gas in layers around a core, where nuclear fusion occurs. As its gravity pulls the outermost gas inward, Polaris develops an opaque layer just under the surface that doesn't let light through easily, dimming its glow. Light then builds up beneath this layer and pushes on it like water vapor boiling up under the lid on a saucepan. That light heats the opaque layer, causing it to expand and making it more transparent. The star becomes bigger and brighter until those outer layers of gas fall inward again and the cycle begins anew.
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Even that 4-day pulsation isn't constant: In 1844, it was about 12 minutes slower than it is now. Previously, astronomer David Turner of St. Mary's University in Halifax, Canada, who was not involved in the new analysis, and colleagues compiled an archive including historical measurements of the pulse. Their data set ended in 2004. Neilson and collaborators, including two citizen astronomers, have now added their own observations from the past decade. This long record, from 1844 to the present, shows that the pulse of Polaris runs about 4.5 seconds slower every year.
The changing rate suggests that the structure of the star is evolving. If, as Neilson and collaborators assume, Polaris is an older star that is fusing or "burning" helium nuclei in its core, then its pulse is decreasing too quickly to match the standard model for stellar evolution. "Only if the star is losing a lot of mass can that [discrepancy] be resolved," Neilson says. This mass may leave Polaris's surface in waves, pushed outward as the pent-up light bursts through the opaque layer, and the loss would slow down the star's pulse rate. To account for the relatively lethargic pulse, Polaris must be losing nearly the equivalent of Earth's mass—or a little under a millionth of its own mass—each year, the team reports in the 1 February issue of The Astrophysical Journal Letters. But never fear, Neilson doesn't think our beacon is hurtling toward oblivion. "Odds are [the mass loss] is episodic," he says.
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Done deal? Maybe not, Turner says. The mass-loss argument hinges on the internal behavior of the pulsing star, and Neilson's team assumes that its layers are moving out of sync—when the outer layers are falling in, the inner layers are pushing out and vice versa. Turner suspects that Polaris is pulsing in a simpler way, with both inner and outer layers moving in the same direction, a hypothesis that his team revived in 2005. In this picture, he says, the North Star's changing pulse can fit the models without hemorrhaging mass because the star is in an earlier stage of its evolution—it's not yet burning helium but is instead preparing to blow up as red giant when the core runs out of hydrogen. On the other hand, if Polaris pulses the way Neilson's team describes it, then the North Star would be past the red giant stage and now burning helium in its core.
Polaris's distance from Earth is the key to figuring out which way it pulsates—and its place in stellar evolution. The more complicated pulse would mean that Polaris shines brighter in absolute terms, so to match its observed brightness in the sky, it would have to be farther away than if the pulse was simple. The Hubble telescope should be able to determine whether the North Star is closer to 325 light-years away, supporting Turner's case, or 425 light-years away, supporting Neilson's. "There are many mysteries about Polaris that defy simple explanation," Turner says. "I think I will sit on the fence in this case and await further observational results."
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3-D Vision for Tiny Eyes
by Elsa Youngsteadt on 26 January 2012, 2:15 PM
摘自http://news.sciencemag.org/sciencenow/2012/01/3-d-vision-for-tiny-eyes.html
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With their keen vision and deadly-accurate pounce, jumping spiders are the cats of the invertebrate world. For decades, scientists have puzzled over how the spiders' miniature nervous systems manage such sophisticated perception and hunting behavior. A new study of Adanson's jumping spider (Hasarius adansoni) fills in one key ingredient: an unusual form of depth perception.
Like all jumping spiders, the Adanson's spider has eight eyes. The two big ones, front and center on the spider's "face," have the sharpest vision. They include a lens that projects an image onto the retina—the light-sensitive tissue at the back of the eye. That much is common in animal vision, but the jumping spider's retina takes things a step further: It consists of not one but four distinct layers of light-sensitive cells. Biologists weren't sure what all those layers were for, and research in the 1980s made them even more enigmatic. Studies showed that whenever an object is focused on the base layer, it is out of focus on the next layer up—which would seem to make the spider's vision blurrier rather than sharper.
That led to a "long-standing mystery," says Duane Harland, a biologist who studies spider vision at AgResearch in Lincoln, New Zealand, and who was not involved in the new study. "What's the point of having a retina that's out of focus?" The answer, it turns out, is that having two versions of the same scene—one crisp and one fuzzy—helps spiders gauge the distance to objects like fruit flies and other prey.
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A team of researchers led by biologists Akihisa Terakita, Mitsumasa Koyanagi, and Takashi Nagata of Osaka City University in Japan reached this conclusion after playing a clever trick on the spider's eyes. First, they used a combination of gene expression studies, electrophysiology, and other methods to determine that the bottom two layers of the spider's retina were the most sensitive to green light. Those two layers also responded weakly to red. The spiders are red-green colorblind, though, so to them, Harland says, a bright red object would look the same as a dim green one.
To test the spiders' depth perception, Terakita's team scooped up four Adanson's spiders from around campus. They dabbed black paint on each spider's six secondary eyes to make sure they were only testing depth perception in the two main eyes. Then, inside a tall plastic dish, each spider pounced—or tried to pounce—on several roaming fruit flies under green light or under red light. In the green light, they almost always snatched the flies with a single leap. But under red light, they fell short—sometimes by almost a centimeter, the team reports today in Science. Their jumps covered, on average, only 90% of the actual distance to the target fly.
That color difference was telling. In either lighting, a jumping spider's eye will focus a sharp image of a fly on the first layer of the retina. But, because the lens at the front of the eye bends green light more sharply than red, the image on the second layer turns out fuzzier in green light. Since the less-blurry red images tricked the spiders into thinking that objects were closer than they really were, the experiment suggests that the spiders uses the fuzziness of that secondary image to judge distance. (Ordinarily, the spiders don't get confused in nature because their sensitivity to the green wavelengths in sunlight overwhelms any input from red.)
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自由阅读
Marie Herberstein, a behavioral ecologist at Macquarie University in Sydney, Australia, is convinced that the spiders gain a sense of depth by comparing the clear and fuzzy images projected on the different layers of their complicated retinas. The study makes a "watertight case," she says.
The results not only explain the usefulness of an out-of-focus retina, Harland says, they also provide an exciting example of how half-centimeter-long animals with brains smaller than those of house flies still manage to gather and act on complex visual information. The next step, he adds, will be figuring out how their eyes and brains actually compare those clear and fuzzy images to get a sense of distance.

越障 (817字)
Deception Diet: How Optical Illusions Can Trick Your Appetite
by Ted Burnham
摘自http://www.npr.org/blogs/thesalt/2012/01/28/145865238/deception-diet-how-optical-illusions-can-trick-your-appetite
Think you know how to avoid overeating? Think again.
Research suggests that choices, like how much to eat during a meal, are often made subconsciously. Trouble is, our brains are hard-wired to mislead us in lots of little ways, which can have a big impact on our diets.
Take the Delboeuf effect, an optical illusion first documented in 1865. It starts with two dots of equal size. But surround one dot with a large circle and the other dot with a small one, and suddenly the second dot looks bigger.
Every time you fill your plate, the Delboeuf illusion affects how much food you take, and how much food you think you've taken, Koert Van Ittersum, professor of marketing at Georgia Tech, tells The Salt.
He and Brian Wansink, director of the Food and Brand Lab at Cornell, performed a series of experiments to measure the effect of the Delboeuf illusion on serving behavior and perceptions of serving size. Their work recently appeared online in the Journal of Consumer Research.
For one experiment, participants were asked to re-create a "target" serving of soup in bowls of various sizes. In another, they had to compare pre-filled bowls to the target serving. Researchers also measured serving behavior in the real-world atmosphere of a buffet line.
As predicted by the illusion, people underserved and overestimated on small dishes, while the reverse was true for large dishes. People using the smallest dishes undershot the target serving by as much as 12 percent. But people using the largest dishes took up to 13 percent more food than they intended.
"We are oftentimes our own worst enemy. And that's not because we want to overeat," Van Ittersum says. The illusion is embedded so deeply in our brains, he says, it is nearly impossible to overcome. Even telling test subjects about it ahead of time, as they did in another phase of the research, didn't eliminate the bias.
The Delboeuf illusion is just one of many subconscious biases influencing our food choices. We may not be able to prevent these kinds of effects, but with a little planning, we could turn them to our advantage. The Salt scoured the literature and came up with these suggestions for eating just enough.
Buy smaller dishes. The average size of an American dinner plate has increased almost 23 percent since 1900, according to Wansink and Van Ittersum. They've shown that people using smaller dishes overestimate the size of their servings, even as they serve themselves less food. Contrasting colors between the food and dish, and between the dish and table, enhance the effect.
Buy taller glasses. Another optical trick, the T-illusion, which you can try for yourself, affects the serving size of liquids. We tend to overestimate vertical lengths, compared with horizontal lengths. In a previous experiment, Wansink and Van Ittersum asked people to pour equal amounts into a short, wide glass and a tall, skinny one. They found that even professional bartenders poured too much into the short, wide glass — but thought the underfilled tall glass held more.
Put healthy food at eye level in your kitchen. In 2010, the cafeteria at Massachusetts General Hospital adopted a green-yellow-red labeling system to indicate how healthy each food was. A few months later, they rearranged the shelves to place healthier items at eye level. Both changes increased purchases of healthy food.
"We were trying to make the default or the easy choice the one that was healthier," says hospital researcher Anne Thorndike, who led the reorganization.
Color-coding might be overkill at home, but you can rearrange your fridge and cabinets to make healthy foods more visible and accessible, and keep unhealthy foods out of sight.
Avoid food porn. It should be a no-brainer that looking at images of delicious food will make you hungry, but science has finally proved it. Researchers in Germany found that looking at pictures of food increases levels of the hormone ghrelin, which makes us feel hungrier and eat more.
Use food coloring. Color affects taste, as our sister blog Shots reported last year. We expect red things to be sweet, like ripe fruit. Cut a few calories by replacing some of the sugar in your recipes with red dye, a food psychologist recommends.
Eat with men. In October, The Salt reported that college students of both genders ate fewer calories in the presence of men than with women. Researchers speculate that social gender norms are to blame: Women may try to eat daintily around men, while men may feel less inclined to show off by pigging out if no women are around.
Adopt a mindful eating routine. OK, so this one isn't subconscious. But several experts reminded The Salt that subliminal tricks only go so far. So slow down and pay attention to your food — and your appetite — as an additional defense against overeating.

xinnono

今天找了几篇science文章给大家换换口味~ 我还没有读, 但是帖的时候觉得越障可能会有点儿简单~ 如果真是这样, 大家就计时当作速度一并做了吧~

miss绿光

谢谢奉献的人儿们~~绿光也决定来跟着每天越障啦~看看规则去~

xinnono

绿光加油哦!

铁板神猴

thx 这个留给明天做~

xeyyxzty

1'18''1'11''
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4'20''
illusions may affect appetites
an illusion: 一样大小的圆点在小圆中看起来比大圆中大~the same with the size of dishes and food
an experiment: offer volunteers the same amount of food in different plates with different sizes,大盘子的人吃得多，小盘子的吃得少
the bias is hard to control
to live healthy~
eat with smaller plates~put healthy food at the 目光的高度~have meals with males~use the knowledge of color~have meals routinely~when you look at some pictures about food, you may eat less

泾渭不凡

1'12''
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自由阅读：33''

......................今天滴真心弱啊，不太明白啊，需要精度，谢谢LZ！...............................

抓抓sandra

抓来给大家加个油!~~

vane914

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xinnono

抓来给大家加个油!~~

-- by 会员 抓抓sandra (2012/1/29 22:54:09)

抓抓来看大家呀! 开心!