雅思阅读模拟试题.docx
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1、 雅思阅读模拟试题 Suns fickle heart may leave us cold 25 January 2023 From New Scientist Print Edition. Stuart Clark 1.Theres 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 phys
2、icist who has created a computer model of our stars core. 2.Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled the effect of temperature fluctuations in the suns interior.According to the standard view, the temperature of the suns core is held constant by the opposing pressures
3、 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 2023, Grandpierre and a collaborator, Gbor goston, calculated that mag
4、netic fields in the suns core could produce small instabilities in the solar plasma.These instabilities would induce localised oscillations in temperature. 4.Ehrlichs model shows that whilst most of these oscillations cancel each other out, some reinforce one another and become long-lived temperatur
5、e variations.The favoured frequencies allow the suns 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 suns magnetic field could flip the fluctuations from one cycle le
6、ngth to the other. 5.These two timescales are instantly recognisable to anyone familiar with Earths 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 resu
7、lt of subtle changes in Earths orbit, known as the Milankovitch cycles.One such cycle describes the way Earths 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, tri
8、ggering 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 a
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