快速導航
學歷類
職業資格
公務員
醫衛類
建筑工程
外語類
外貿類
計算機類
財會類
技能鑒定
1 There's a dimmer switch inside the sun that causes its brightness to rise
and fall on timescales of around 100,000 years - exactly the same period as
between ice ages on Earth. So says a physicist who has created a computer model
of our star's core.
2 Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled
the effect of temperature fluctuations in the sun's interior. According to the
standard view, the temperature of the sun's core is held constant by the
opposing pressures of gravity and nuclear fusion. However, Ehrlich believed that
slight variations should be possible.
3 He took as his starting point the work of Attila Grandpierre of the Konkoly
Observatory of the Hungarian Academy of Sciences. In 2005, Grandpierre and a
collaborator, Gábor ágoston, calculated that magnetic fields in the sun's core
could produce small instabilities in the solar plasma. These instabilities would
induce localised oscillations in temperature.
4 Ehrlich's model shows that whilst most of these oscillations cancel each
other out, some reinforce one another and become long-lived temperature
variations. The favoured frequencies allow the sun's core temperature to
oscillate around its average temperature of 13.6 million kelvin in cycles
lasting either 100,000 or 41,000 years. Ehrlich says that random interactions
within the sun's magnetic field could flip the fluctuations from one cycle
length to the other.
5 These two timescales are instantly recognisable to anyone familiar with
Earth's ice ages: for the past million years, ice ages have occurred roughly
every 100,000 years. Before that, they occurred roughly every 41,000 years.
6 Most scientists believe that the ice ages are the result of subtle changes
in Earth's orbit, known as the Milankovitch cycles. One such cycle describes the
way Earth's orbit gradually changes shape from a circle to a slight ellipse and
back again roughly every 100,000 years. The theory says this alters the amount
of solar radiation that Earth receives, triggering the ice ages. However, a
persistent problem with this theory has been its inability to explain why the
ice ages changed frequency a million years ago.
7 "In Milankovitch, there is certainly no good idea why the frequency should
change from one to another," says Neil Edwards, a climatologist at the Open
University in Milton Keynes, UK. Nor is the transition problem the only one the
Milankovitch theory faces. Ehrlich and other critics claim that the temperature
variations caused by Milankovitch cycles are simply not big enough to drive ice
ages.
8 However, Edwards believes the small changes in solar heating produced by
Milankovitch cycles are then amplified by feedback mechanisms on Earth. For
example, if sea ice begins to form because of a slight cooling, carbon dioxide
that would otherwise have found its way into the atmosphere as part of the
carbon cycle is locked into the ice. That weakens the greenhouse effect and
Earth grows even colder.
9 According to Edwards, there is no lack of such mechanisms. "If you add
their effects together, there is more than enough feedback to make Milankovitch
work," he says. "The problem now is identifying which mechanisms are at work."
This is why scientists like Edwards are not yet ready to give up on the current
theory. "Milankovitch cycles give us ice ages roughly when we observe them to
happen. We can calculate where we are in the cycle and compare it with
observation," he says. "I can't see any way of testing [Ehrlich's] idea to see
where we are in the temperature oscillation."
10 Ehrlich concedes this. "If there is a way to test this theory on the sun,
I can't think of one that is practical," he says. That's because variation over
41,000 to 100,000 years is too gradual to be observed. However, there may be a
way to test it in other stars: red dwarfs. Their cores are much smaller than
that of the sun, and so Ehrlich believes that the oscillation periods could be
short enough to be observed. He has yet to calculate the precise period or the
extent of variation in brightness to be expected.
11 Nigel Weiss, a solar physicist at the University of Cambridge, is far from
convinced. He describes Ehrlich's claims as "utterly implausible". Ehrlich
counters that Weiss's opinion is based on the standard solar model, which fails
to take into account the magnetic instabilities that cause the temperature
fluctuations.
Questions 1-4
Complete each of the following statements with One or Two names of the
scientists from the box below.
Write the appropriate letters A-E in boxes 1-4 on your answer sheet.
A. Attila Grandpierre
B. Gábor ágoston
C. Neil Edwards
D. Nigel Weiss
E. Robert Ehrlich
1. ...claims there a dimmer switch inside the sun that causes its brightness
to rise and fall in periods as long as those between ice ages on Earth.
2. ...calculated that the internal solar magnetic fields could produce
instabilities in the solar plasma.
3. ...holds that Milankovitch cycles can induce changes in solar heating on
Earth and the changes are amplified on Earth.
4. ...doesn't believe in Ehrlich's viewpoints at all.
Questions 5-9
Do the following statements agree with the information given in the reading
passage?
In boxes 5-9 on your answer sheet write
TRUE if the statement is true according to the passage
FALSE if the statement is false according to the passage
NOT GIVEN if the information is not given in the passage
5. The ice ages changed frequency from 100,000 to 41,000 years a million
years ago.
6. The sole problem that the Milankovitch theory can not solve is to explain
why the ice age frequency should shift from one to another.
7. Carbon dioxide can be locked artificially into sea ice to eliminate the
greenhouse effect.
8. Some scientists are not ready to give up the Milankovitch theory though
they haven't figured out which mechanisms amplify the changes in solar
heating.
9. Both Edwards and Ehrlich believe that there is no practical way to test
when the solar temperature oscillation begins and when ends.
Questions 10-14
Complete the notes below.
Choose one suitable word from the Reading Passage above for each answer.
Write your answers in boxes 10-14 on your answer sheet.
The standard view assumes that the opposing pressures of gravity and nuclear
fusions hold the temperature ...10...in the sun's interior, but the slight
changes in the earth's ...11... alter the temperature on the earth and cause ice
ages every 100,000 years. A British scientist, however, challenges this view by
claiming that the internal solar magnetic ...12... can induce the temperature
oscillations in the sun's interior. The sun's core temperature oscillates around
its average temperature in ...13... lasting either 100,000 or 41,000 years. And
the ...14... interactions within the sun's magnetic field could flip the
fluctuations from one cycle length to the other, which explains why the ice ages
changed frequency a million years ago.
主站蜘蛛池模板：
一区二区三区在线 | 欧洲|
久久视频这里只精品99|
国产高潮国产高潮久久久|
强制高潮18xxxxhd日韩|
午夜dj视频在线观看完整版1|
国产成人无码www免费视频播放|
欧美亚洲综合久久偷偷人人|
久久丫精品忘忧草西安产品|
欧美超级乱婬视频播放|
欧美猛少妇色xxxxx猛叫|
成年无码a√片在线观看|
久久综合亚洲色一区二区三区|
日本少妇高潮喷水视频|
无码欧美黑人xxx一区二区三区|
狠狠色狠狠色综合网|
久久人妻|
无码一区二区三区亚洲人妻|
秋霞午夜成人鲁丝片午夜精品|
夜夜爱夜鲁夜鲁很鲁|
国产内射爽爽大片视频社区在线|
无码人妻精品一区二区三区免费|
无码高潮爽到爆的喷水视频|
亚洲国产日韩a在线亚洲|
久久人妻公开中文字幕|
国色天香中文字幕在线视频|
日韩人妻无码精品系列|
亚洲精品国产精品乱码不卞|
熟妇人妻一区二区三区四区|
色偷偷亚洲第一综合网|
国产精品高潮呻吟av久久无吗|
成人做爰视频www网站小优视频|
亚洲午夜成人精品电影在线观看|
亚洲乱码中文字幕久久孕妇黑人|
双腿张开被9个男人调教|
狠狠色丁香婷婷综合潮喷|
少妇高潮无套内谢麻豆传|
亚洲欧美综合在线中文|
免费精品99久久国产综合精品|
天天影视网色香欲综合网|
人人妻人人添人人爽日韩欧美|
18无码粉嫩小泬无套在线观看|
