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1、雅思阅读实战：Sun'sfickleheartmayleaveuscold北京语言大学雅思培训中心即日起与“无忧雅思”合作，向“无忧雅思”的网友提供在难度、长度、题材、题型方面与雅思考试近似的练习。这些练习，均以最新的国外报刊上的文章为素材，按雅思阅读的题型，出题并提供答案及简单注释。欢迎网友积极使用。北京语言大学雅思培训中心编写的教材，以质量著称。本栏目的所有练习，仅为“无忧雅思”网友个人使用。希望各个培训机构、培训教师及出版机构尊重北京语言大学雅思培训中心教师的劳动，不要盗用。 Sun'sfic
2、kleheartmayleaveuscold 25January2007 FromNewScientistPrintEdition. StuartClark1 There'sadimmerswitchinsidethesunthatcausesitsbrightnesstoriseandfallontimescalesofaround100,000years-exactlythesameperiodasbetweeniceagesonEarth.Sosaysaphysi
3、cistwhohascreatedacomputermodelofourstar'score.2 RobertEhrlichofGeorgeMasonUniversityinFairfax,Virginia,modelledtheeffectoftemperaturefluctuationsinthesun'sinterior.Accordingtothestandardview,thetemperatureofthesun'scoreisheldconstantbytheopposingpress
4、uresofgravityandnuclearfusion.However,Ehrlichbelievedthatslightvariationsshouldbepossible.3 HetookashisstartingpointtheworkofAttilaGrandpierreoftheKonkolyObservatoryoftheHungarianAcademyofSciences.In2005,Grandpierreandacollaborator,GáborÁgoston,calcula
5、tedthatmagneticfieldsinthesun'scorecouldproducesmallinstabilitiesinthesolarplasma.Theseinstabilitieswouldinducelocalisedoscillationsintemperature.4 Ehrlich'smodelshowsthatwhilstmostoftheseoscillationscanceleachotherout,somereinforceoneanotherandbecomel
6、ong-livedtemperaturevariations.Thefavouredfrequenciesallowthesun'scoretemperaturetooscillatearounditsaveragetemperatureof13.6millionkelvinincycleslastingeither100,000or41,000years.Ehrlichsaysthatrandominteractionswithinthesun'smagneticfieldcouldflipthe
7、fluctuationsfromonecyclelengthtotheother.5 ThesetwotimescalesareinstantlyrecognisabletoanyonefamiliarwithEarth'siceages:forthepastmillionyears,iceageshaveoccurredroughlyevery100,000years.Beforethat,theyoccurredroughlyevery41,000years.6 Mostscientistsbe
8、lievethattheiceagesaretheresultofsubtlechangesinEarth'sorbit,knownastheMilankovitchcycles.OnesuchcycledescribesthewayEarth'sorbitgraduallychangesshapefromacircletoaslightellipseandbackagainroughlyevery100,000years.Thetheorysaysthisalter
