考研英语冲刺作文.docx

考研英语冲刺作文TheinventionoftheincandescentlightbulbbyThomasA.Edisonin1879createdademandforacheap,readilyavailablefuelwithwhichtogeneratelargeamountsofelectricpower.Coalseemedtofitthebill,anditfueledtheearliestpowerstations.(whichweresetupattheendofthenineteenthcenturybyEdisonhimself).Asmorepowerplantswereconstructedthroughoutthecountry,therelianceoncoalincreasedthroughoutthecountry,therelianceoncoalincreased.SincetheFirstWorldWar,coal-firedpowerplantshadacombinedintheUnitedStateseachyear.In1986suchplantshadacombinedgeneratingcapacityof289,000megawattsandconsumed83percentofthenearly900milliontonsofcoalminedinthecountrythatyear.Giventheuncertaintyinthefuturegrowthofthenearly900milliontonsofcoalminedinthecountrythatyear.Giventheuncertaintyinthefuturegrowthofnuclearpowerandinthesupplyofoilandnaturalgas,coal-firedpowerplantscouldwellprovideupto70percentoftheelectricpowerintheUnitedStatesbytheendofthecentury.Yet,inspiteofthefactthatcoalhaslongbeenasourceofelectricityandmayremainonformanyyears(coalrepresentsabout80percentofUnitedStatesfossil-fuelreserves),ithasactuallyneverbeenthemostdesirablefossilfuelforpowerplants.Coalcontainslessenergyperunitofweightthanweightthannaturalgasoroil;itisdifficulttotransport,anditisassociatedwithahostofenvironmentalissues,amongthemacidrain.Sincethelate1960sproblemsofemissioncontrolandwastedisposalhavesharplyreducedtheappealofcoal-firedpowerplants.Thecostofamelioratingtheseenvironmentproblemsalongwiththerisingcostofbuildingafacilityaslargeandcomplexasacoal-firedpowerplant,havealsomadesuchplantslessattractivefromapurelyeconomicperspective.Changesinthetechnologicalbaseofcoal-firedpowerplantscouldrestoretheirattractiveness,however.Whereassomeofthesechangesareintendedmainlytoincreasetheproductivityofexistingplants,completelynewtechnologiesforburningcoalcleanlyarealsobeingdeveloped.Asummaryofthephysicalandchemicalnatureoflifemustbegin,notontheEarth,butintheSun;infact,attheSunsverycenter.ItisherethatistobefoundthesourceoftheenergythattheSunconstantlypoursoutintospaceaslightandheat.ThisenergyislibratedatthecenteroftheSunasbillionsuponbillionsofnucleiofhydrogenatomscollidewitheachotherandfusetogethertoformnucleiofhelium,andindoingso,releasesomeoftheenergythatisstoredinthenucleiofatoms.TheoutputoflightandheatoftheSunrequiresthatsome600milliontonsofhydrogenbeconvertedintoheliumintheSuneverysecond.ThistheSunhasbeendoingforseveralthousandsofmillionsofyear.ThenuclearenergyisreleasedattheSunscenterashigh-energygammaradiation,aformofelectromagneticradiationlikelightandradiowaves,onlyofverymuchshorterwavelength.ThisgammaradiationisabsorbedbyatomsinsidetheSuntobereemittedatslightlylongerwavelengths.Thisradiation,initsturnisabsorbedandreemitted.Astheenergyfiltersthroughthelayersofthesolarinterior,itpassesthroughtheX-raypartofthespectrumeventuallybecominglight.Atthisstage,ithasreachedwhatwecallthesolarsurface,andcanescapeintospacewithoutbeingabsorbedfurtherbysolaratoms.AverysmallfractionoftheSunslightandheatisemittedinsuchdirectionsthatafterpassingunhinderedthroughinterplanetaryspace,ithitstheEarth.Theconceptofobtainingfreshwaterfromicebergsthataretowedtopopulatedareasandaridregionsoftheworldwasoncetreatedasajokemoreappropriatetocartoonsthanreallife.Butnowitisbeingconsideredquiteseriouslybymanynations,especiallysincescientistshavewarnedthatthehumanracewilloutgrowitsfreshwatersupplyfasterthanitrunsoutoffood.Glaciersareapossiblesourceoffreshwaterthathasbeenoverlookeduntilrecently.Three-quartersoftheEarthsfreshwatersupplyisstilltiedupinglacialice,areservoirofuntappedfreshwatersoimmensethatitcouldsustainalltheriversoftheworldfor1,000years.Floatingontheoceanseveryyearare7,659trillionmetrictonsoficeencasedin10000icebergsthatbreakawayfromthepolaricecaps,morethanninetypercentofthemfromAntarctica.Hugeglaciersthatstretchovertheshallowcontinentalshelfgivebirthtoicebergsthroughouttheyear.Icebergsarenotlikeseaice,whichisformedwhentheseaitselffreezes,rather,theyareformedentirelyonland,breakingoffwhenglaciersspreadoverthesea.Astheydriftawayfromthepolarregion,icebergssometimesmovemysteriouslyinadirectionoppositetothewind,pulledbysubsurfacecurrents.Becausetheymeltmoreslowlythansmallerpiecesofice,icebergshavebeenknowntodriftasfarnorthas35degreessouthoftheequatorintheAtlanticOcean.Tocorralthemandsteerthemtopartsoftheworldwheretheyareneededwouldnotbetoodifficult.Thedifficultyarisesinothertechnicalmatters,suchasthepreventionofrapidmeltinginwarmerclimatesandthefunnelingoffreshwatertoshoreingreatvolume.Buteveniftheicebergslosthalfoftheirvolumeintowing,thewatertheycouldprovidewouldbefarcheaperthanthatproducedbydesalinization,orremovingsaltfromwater。

Afolkcultureisasmallisolated,cohesive,conservative,nearlyself-sufficientgroupthatishomogeneousincustomandracewithastrongfamilyorclanstructureandhighlydevelopedrituals.Orderismaintainedthroughsanctionsbasedinthereligionorfamilyandinterpersonal.Relationshipsarestrong.Traditionisparamount,andchangecomesinfrequentlyandslowly.Thereisrelativelylittledivisionoflaborintospe。