2015年轉瞬就要迎來7月份的測驗，對付預備後半年雅思測驗的“烤鴨”們來講，現在多演習，積聚瀏覽量照樣很主要的，小編為考生們整頓了雅思測驗瀏覽相幹模仿題，願望眾人可以或許在賡續的演習中瀏覽才能獲得晉升!
Sun's fickle heart may leave us cold
□ 25 January 2007
□ From New Scientist Print Edition.
□ Stuart Clark
1 There's a dimmer switch inside the sun thatcauses its brightness to rise and fall on timescales ofaround 100,000 years - exactly the same period asbetween ice ages on Earth. So says a physicist whohas created a computer model of our star's core.
2 Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled the effect oftemperature fluctuations in the sun's interior. According to the standard view, thetemperature of the sun's core is held constant by the opposing pressures of gravity andnuclear 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 ofthe 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 solarplasma. These instabilities would induce localised oscillations in temperature.
4 Ehrlich's model shows that whilst most of these oscillations cancel each other out, somereinforce one another and become long-lived temperature variations. The favouredfrequencies allow the sun's core temperature to oscillate around its average temperature of13.6 million kelvin in cycles lasting either 100,000 or 41,000 years. Ehrlich says that randominteractions within the sun's magnetic field could flip the fluctuations from one cycle length tothe 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 graduallychanges 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 iceages. However, a persistent problem with this theory has been its inability to explain why theice ages changed frequency a million years ago.
7 "In Milankovitch, there is certainly no good idea why the frequency should change fromone 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 othercritics claim that the temperature variations caused by Milankovitch cycles are simply not bigenough to drive ice ages.
8 However, Edwards believes the small changes in solar heating produced by Milankovitchcycles are then amplified by feedback mechanisms on Earth. For example, if sea ice begins toform because of a slight cooling, carbon dioxide that would otherwise have found its way intothe atmosphere as part of the carbon cycle is locked into the ice. That weakens thegreenhouse effect and Earth grows even colder.
9 According to Edwards, there is no lack of such mechanisms. "If you add their effectstogether, there is more than enough feedback to make Milankovitch work," he says. "Theproblem now is identifying which mechanisms are at work." This is why scientists like Edwardsare not yet ready to give up on the current theory. "Milankovitch cycles give us ice agesroughly when we observe them to happen. We can calculate where we are in the cycle andcompare it with observation," he says. "I can't see any way of testing [Ehrlich's] idea to seewhere 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 ofone that is practical," he says. That's because variation over 41,000 to 100,000 years is toogradual to be observed. However, there may be a way to test it in other stars: red dwarfs. Theircores are much smaller than that of the sun, and so Ehrlich believes that the oscillation periodscould be short enough to be observed. He has yet to calculate the precise period or theextent of variation in brightness to be expected.
11 Nigel Weiss, a solar physicist at the University of Cambridge, is far from convinced. Hedescribes Ehrlich's claims as "utterly implausible". Ehrlich counters that Weiss's opinion isbased on the standard solar model, which fails to take into account the magnetic instabilitiesthat cause the temperature fluctuations.
(716 words)
Questions 1-4
Complete each of the following statements with One or Two names of the scientists fromthe box below.
Write the appropriate letters A-E in boxes 1-4 on your answer sheet.
1. ...claims there‘s a dimmer switch inside the sun that causes its brightness to rise and fallin periods as long as those between ice ages on Earth.
2. ...calculated that the internal solar magnetic fields could produce instabilities in thesolar plasma.
3. ...holds that Milankovitch cycles can induce changes in solar heating on Earth and thechanges 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 agefrequency 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'tfigured 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 solartemperature 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 fusionshold 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 Britishscientist, however, challenges this view by claiming that the internal solar magnetic ...12... caninduce the temperature oscillations in the sun's interior. The sun's core temperatureoscillates 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 onecycle length to the other, which explains why the ice ages changed frequency a million yearsago.
Answer keys and explanations:
1. E
See the sentences in paragraph 1(There's adimmer switch inside the sun that causes itsbrightness to rise and fall on timescales of around100,000 years - exactly the same period as betweenice ages on Earth. So says a physicist who hascreated a computer model of our star's core.) andpara.2 (Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled the effect oftemperature fluctuations in the sun's interior.)
2. A B
See para.3: ?i style='mso-bidi-font-style: normal'>Grandpierre and a collaborator,Gábor ágoston, calculated that magnetic fields in the sun's core could produce smallinstabilities in the solar plasma.
3. C
See para.8: Edwards believes the small changes in solar heating produced by Milankovitchcycles are then amplified by feedback mechanisms on Earth.
4. D
See para.11: Nigel Weiss, a solar physicist at the University of Cambridge, is far fromconvinced. He describes Ehrlich's claims as "utterly implausible".
5. False
See para.5: for the past million years, ice ages have occurred roughly every 100,000 years.Before that, they occurred roughly every 41,000 years.
6. False
See para.7: "In Milankovitch, there is certainly no good idea why the frequency shouldchange from one to another," ... Nor is the transition problem the only one the Milankovitchtheory faces.
7. Not Given
See para.8: if sea ice begins to form because of a slight cooling, carbon dioxide?is lockedinto the ice. That weakens the greenhouse effect. (The passage doesn抰 mention anythingabout locking Co2 into ice artificially.)
8. True
See para.9: there is no lack of such mechanisms. "If you add their effects together, there ismore than enough feedback to make Milankovitch work,"?"The problem now is identifying whichmechanisms are at work." This is why scientists like Edwards are not yet ready to give up onthe current theory.
9. True
See the sentences in para.9 (According to Edwards, 卙e says. "I can't see any way oftesting [Ehrlich's] idea to see where we are in the temperature oscillation.") and para.10 (Ehrlich concedes this. "If there is a way to test this theory on the sun, I can't think of one thatis practical).
10. constant
See para.2: According to the standard view, the temperature of the sun's core is heldconstant by the opposing pressures of gravity and nuclear fusion.
11. orbit
See para.6: Most scientists believe that the ice ages are the result of subtle changes inEarth's orbit, 匛arth's orbit gradually changes shape from a circle to a slight ellipse and backagain roughly every 100,000 years.
12. instabilities
See para.3: ?i style='mso-bidi-font-style:normal'>magnetic fields in the sun's corecould produce small instabilities in the solar plasma. These instabilities would induce localisedoscillations in temperature.
13. cycles
See para.4: …allow the sun's core temperature to oscillate around its averagetemperature of 13.6 million kelvin in cycles lasting either 100,000 or 41,000 years.
14. random
See para.4: Ehrlich says that random interactions within the sun's magnetic field could flipthe fluctuations from one cycle length to the other.
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