概括大意打印.docx

概括大意打印.docx

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概括大意打印

第十一篇TheTiniestElectricMotorintheWorld

1Scientistsrecentlymadepublicthetiniestelectricmotorever1built.Youcouldstuffhundredsofthemintotheperiodattheendofthissentence.Onedayasimilarenginemightpoweratinymechanicaldoctorthatwouldtravelthroughyourbodytoremoveyourdisease.

2Themotorworksbyshufflingatomsbetweentwomoltenmetaldropletsinacarbonnanotube.Onedropletisevensmallerthantheother.Whenasmallelectriccurrentisappliedtothedroplets,atomsslowlygetoutofthelargerdropletandjointhesmallerone.Thesmalldropletgrows—butnevergetsasbigastheotherdroplet—andeventuallybumpsintothelargedroplet.Astheytouch,thelargedropletrapidlysopsuptheatomsithadpreviouslylost.Thisquickshiftinenergyproducesapowerstroke2.

3Thetechniqueexploitsthefactthatsurfacetension—thetendencyofatomsormoleculestoresistseparating—becomesmoreimportantatsmallscales3.Surfacetensionisthesamethingthatallowssomeinsectstowalkonwater.

4Althoughtheamountofenergyproducedissmall—20microwatts—itisquiteimpressiveinrelationtothetinyscaleofthemotor4.Thewholesetup5islessthan200nanometersonaside,orhundredsoftimessmallerthanthewidthofahumanhair.Ifitcouldbescaleduptothesizeofanautomobileengine6,itwouldbetoomilliontimesmorepowerfulthanaToyotaCamry’s225horsepowerV6engine.

5In1988,ProfessorRichardMullerandcolleaguesmadethefirstoperatingmicromotor,whichwas100micronsacross7,oraboutthethicknessofahumanhair.In2003,Zettl’sgroupcreatedthefirstnanoscalemotor.In2006,theybuiltananoconveyor,whichmovestinyparticlesalonglikecarsinafactory.

6Nanotechnologyengineerstrytomimicnature,buildingthingsatom-by-atom.Amongotherthings,nanomotorscouldbeusedinopticalcircuitstoredirectlight,aprocesscalledopticalswitching.Futuristsenvisionadaywhennanomachines,poweredbynanomotors,travelinsideyourbodytofinddiseaseandrepairdamagedcells.

1.Paragraph2TheWorkingPrincipleoftheNanomotor

2.Paragraph4ADescriptionoftheNanomotorinTermsofPowerandSize

3.Paragraph5PreviousInventionsofNanoscaleProducts

4.Paragraph6PossibleFieldsofApplicationintheFuture

5.Doctorsenvisionthatthenanomotorwouldtravelthroughhumanbodiesto.

emovedisease

6.Surfacetensionmeansthetendencyofatomsormoleculesto

resistseparating.

7.Nanoconveyorscouldbeusedto.

transportnanoscaleobjects

8.Applyingasmallelectriccurrentcausesatomsto.

shufflebetweentwomoltenmetaldroplets

第十二篇AStrongGreenhouseGas

1Methaneisacolorless,odorlessgas;itisalsoapotentgreenhousegas,andoncereleasedintotheatmosphere1,itabsorbsheatradiatingfromEarth’ssurface.That’swhymethaneisamajorcontributortotheplanet’sincreasingtemperaturerise—orglobalwarming.Moleculeformolecule,methane’sheat-trappingpowerintheatmosphereis21timesstrongerthancarbondioxide2,themostabundantgreenhousegas.

2With13billioncowsbelchingalmostconstantlyaroundtheworld（100millionintheU.S.alone）,it’snosurprisethatmethanereleasedbylivestockisoneofthechiefglobalsourcesofthegas.Otherprimemethanesources:

petroleum,drilling,coalmining,solid-wastelandfillsandwetlands.

3GreenhousegaseslikemethaneandcarbondioxidemakeuponlyasmallpartofEarth’satmosphere,whichis78percentnitrogenandnearly21percentoxygen.Andwithoutgreenhousegasestotrapthesun’sheatandwarmtheplanet,lifeasweknowitcouldn’texist3.Butinthelast200years,humanactivitythatrequiresburningoil,naturalgas,andcoalforenergyhasmagnifiedthegreenhouseeffect.

4Atmosphericconcentrationsofmethanehavemorethandoubledinthelasttwocenturies.Blameforthisoftenfocusesonbigindustriesandgas-guzzlingvehicles.Butagricultureplaysamajorrole,too.Inthepast40yearsalone,theglobalcattlepopulationhasdoubled.

5Cowsmunchmostlygrassesandhay—yettheygrowbigandhefty.Why?

Becauseoftherumen.The

rumenholds160litersoffoodandbillionsofmicrobes.Thesemicroscopicbacteriaandbreakdowncelluloseandfiberintodigestiblenutrients.Acowcouldn’tlivewithoutitsmicrobes.Asthemicrobesdigestcellulose,theyreleasemethane.Theprocessoccursinallanimalswitharumen（cows,sheep,andgoats,forexample）,anditmakethemverygassy.It’spartoftheirnormaldigestionprocess.Whentheychewtheircud,theyregurgitatesomefoodtorechewit,andallthisgascomesout.Theaveragecowexpels600litersofmethaneaday.

6That’swhywesaylivestockgasisalsoamajorfactorofcausingtheglobalwarming.

1.Paragraph1MethaneasaStrongGreenhouseGas

2.Paragraph2Livest