新概念第四冊(cè)lesson66講義Cohesion-tensionTheoryCohesion1-tensionTheoryAtmospheric2pressurecansupportacolumnofwaterupto10metershigh.Butplantscanmovewatermuchhigher;thesequoia3treecanpumpwatertoitsverytopmorethan100metersabovetheground.Untiltheendofthenineteenthcentury,themovementofwaterintreesandothertallplantswasamystery.Somebotanists4hypothesizedthatthelivingcellsofplantsactedaspumps.Butmanyexperimentsdemonstratedthatthestemsofplantsinwhichallthecellsarekilledcanstillmovewatertoappreciable5heights.Otherexplanationsforthemovementofwaterinplantshavebeenbasedonrootpressure,apushonthewaterfromtherootsatthebottomoftheplant.Butrootpressureisnotnearlygreatenoughtopushwatertothetopsoftalltrees.Furthermore,theconifers,whichareamongthetallesttrees,haveunusuallylowrootpressures.Ifwaterisnotpumpedtothetopofatalltree,andifitisnotpushedtothetopofatalltree,thenwemayask:howdoesitgetthere?Accordingtothecurrentlyacceptedcohesion-tensiontheory,waterispulledthere.Thepullonarisingcolumnofwaterinaplantresultsfromtheevaporation6ofwateratthetopoftheplant.Aswaterislostfromthesurfaceoftheleaves,anegativepressure,ortension,iscreated.Theevaporatedwaterisreplacedbywatermovingfrominsidetheplantinunbrokencolumnsthatextendfromthetopofaplanttoitsroots.Thesameforcesthatcreatesurfacetensioninanysampleofwaterareresponsibleforthemaintenanceoftheseunbrokencolumnsofwater.Whenwaterisconfinedintubesofverysmallbore,theforcesofcohesion(theattractionbetweenwatermolecules)aresogreatthatthestrengthofacolumnofwatercompareswiththestrengthofasteelwireofthesamediameter.Thiscohesive7strengthpermitscolumnsofwatertobepulledtogreatheightswithoutbeingbroken.內(nèi)聚壓力理論大氣壓能夠支持10米高的水柱，但植物可將水送得更高。美洲紅杉就能把水泵到地面以上100多米高的樹頂。直到19世紀(jì)末，水在樹木和其它高大植物中的輸送還是一個(gè)謎。一些植物學(xué)家假定植物中的活細(xì)胞充當(dāng)了水泵的角色。但許多實(shí)驗(yàn)表明細(xì)胞都已死亡的植物莖干仍能將水輸送到相當(dāng)可觀的高度。對(duì)于植物中輸送水的其它解釋都基于根壓--植物底端的根對(duì)水的推動(dòng)。但根壓完全不足以將水推到樹頂。況且，最高樹木中的松柏只有很低的根壓。如果水不是被泵到高樹的樹頂，也不是被推到樹頂，那么我們會(huì)問：它是怎樣到達(dá)樹頂?shù)哪?根據(jù)目前為人們所接受的內(nèi)聚壓力的理論，水是被拉到上面去的。一株植物中作用于一個(gè)正在升高的水柱之上的拉力來自該植物頂部水的蒸發(fā)。由于水從葉子表面喪失，一個(gè)負(fù)壓力，或張力就得以產(chǎn)生。蒸發(fā)出去的水被植物里流動(dòng)的水代替。這些水形成水柱從植物頂端一直延伸到根部。在任何水樣中造成表面張力的力支持著這些不斷的水柱。當(dāng)水被限制在內(nèi)徑很小的管道中時(shí)，內(nèi)聚壓力(水分子之間的相互吸引力)是如此之大以致一支水柱的強(qiáng)度相當(dāng)于一根直徑相同的鋼絲的強(qiáng)度。這種內(nèi)聚壓力使得水柱被拉到非常高的地方而不會(huì)斷裂。

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1cohesion

n.團(tuán)結(jié)，凝結(jié)力參考例句：Ihadtobringsomecohesionintothecompany.我得使整個(gè)公司恢復(fù)凝聚力。Thepowerofcultureisdeeplyrootedinthevitality,creativityandcohesionofanation.文化的力量，深深熔鑄在民族的生命力、創(chuàng)造力和凝聚力之中。2atmospheric

adj.大氣的，空氣的；大氣層的；大氣所引起的參考例句：Seasurfacetemperaturesandatmosphericcirculationarestronglycoupled.海洋表面溫度與大氣環(huán)流是密切相關(guān)的。Cloudsreturnradiantenergytothesurfaceprimarilyviatheatmosphericwindow.云主要通過大氣窗區(qū)向地表輻射能量。3sequoia

n.紅杉參考例句：Thesequoianationalforestisatthesouthernendofthesierranevadarange.紅杉國家公園位于內(nèi)華達(dá)山脈南端盡頭處。ThephotoshowstheenormousgeneralShermantreeinCalifornia'ssequoianationalpark.照片顯示的是加利福尼亞州紅杉國家公園內(nèi)巨大的謝爾曼將軍樹。4botanists

n.植物學(xué)家，研究植物的人(botanist的名詞復(fù)數(shù))參考例句：Botanistshadsomedifficultycategorizingthenewlyfoundplant.植物學(xué)家們不大容易確定這種新發(fā)現(xiàn)的植物的種類。來自辭典例句Botanistsreferthisflowertotherosefamily.植物學(xué)家將這花歸入薔薇科。來自辭典例句5appreciable

adj.明顯的，可見的，可估量的，可覺察的參考例句：Thereisnoappreciabledistinctionbetweenthetwins.在這對(duì)孿生子之間看不出有什么明顯的差別。Weboughtanappreciablepieceofproperty.我們買下的資產(chǎn)有增值的潛力。6evaporation

n.蒸發(fā)，消失參考例句：Becarefulnottolosetoomuchliquidbyevaporation.小心不要因蒸發(fā)失去太多水分。Ourbodiescansweat,therebylosingheatbyevaporation.我們的身體能出汗，由此可以蒸發(fā)散熱。7cohesive

adj.有粘著力的；有結(jié)合力的；凝聚性的參考例句：Shesealedtheparcelwithcohesivetape.她用粘膠帶把包裹封起來。Theauthorskillfullyfusesthesefragmentsintoacohesivewhole.作者將這些片斷巧妙地結(jié)合成一個(gè)連貫的整體。AmericanBlackBearsAmericanblackbearsAmericanblackbearsappearinavarietyofcolorsdespitetheirname.Intheeasternpartoftheirrange,mostofthesebrown,red,orevenyellowcoats.Tothenorth,theblackbearisactuallygrayorwhiteincolor.Eveninthesamelitter,bothbrownandblackfurredbearsmaybeborn.BlackbearsarethesmallestofallAmericanbears,ranginginlengthfromfivetosixfeet,weighingfromthreehundredtofivehundredpoundsTheireyesandearsaresmallandtheireyesightandhearingarenotasgoodastheirsenseofsmell.Likeallbears,theblackbearistimid,clumsy,andrarelydangerous,butifattacked,mostcanclimbtreesandcovergroundatgreatspeeds.Whenangryorfrightened,itisaformidableenemy.Blackbearsfeedonleaves,herbs.Fruit,berries,insects,fish,andevenlargeranimals.Oneofthemostinterestingcharacteristicsofbears,includingtheblackbear,istheirwintersleep.Unlikesquirrels,woodchucks,andmanyotherwoodlandanimals,bearsdonotactuallyhibernate1.Althoughthebeardoesnotduringthewintermoths2,sustainingitselffrombodyfat,itstemperatureremains3almostnormal,anditbreathesregularlyfourorfivetimesperminute.Mostblackbearslivealone,exceptduringmatingseason.Theyprefertoliveincaves,hollowlogs,ordense4thickets5.Alittleofonetofourcubs6isborninJanuaryorFebruaryafteragestation7periodofsixtoninemonths,andtheyremainwiththeirmotheruntiltheyarefully8grownoraboutoneandahalfyearsold.Blackbearscanliveaslongasthirtyyearsinthewild,andevenlongeringamepreservessetasideforthem.美國黑熊美國黑熊雖然被叫做黑熊但卻有各種各樣的顏色。在它們生活區(qū)域的東部，大部分黑熊長有富有光澤的黑毛，但在西部，他們則長著棕色、紅色甚至是黃色的毛。在北部，黑熊其實(shí)長著灰色或白色的毛。就是在一胎所生的小熊中，都可能混雜棕毛和黑毛。黑熊是所有美洲熊中最小的，5～6英尺長，300～500磅重。它們的眼睛和耳朵都很小，他們的視力和聽覺不如嗅覺那樣好。像所有的熊一樣，黑熊膽小，笨拙，很少具有危險(xiǎn)性。但如果受到攻擊，大部分黑熊會(huì)以很快的速度爬上樹和奔跑。當(dāng)發(fā)怒或受驚嚇時(shí)，黑熊會(huì)成為可怕的對(duì)手。黑熊以樹葉、草、樹根、水果、漿果、昆蟲、魚，甚至更大的動(dòng)物為食。熊類，包括黑熊的最有趣的一個(gè)特點(diǎn)是他們的冬眠。與松鼠、旱獺和其它別的林地動(dòng)物不同，熊并不真正地冬眠。雖然熊在冬天的幾個(gè)月中不吃東西，靠體內(nèi)脂肪維持生命，但它們的體溫保持正常，并有規(guī)律地一分鐘呼吸4或5次。除交配季節(jié)外，大多數(shù)黑熊獨(dú)自生活。他們喜歡住在洞里、空心的大木頭里或茂密的樹叢里。經(jīng)過6到9個(gè)月的懷孕期后一胎1～4個(gè)小熊在1月或2月出生。它們同母熊住在一起，直到它們完全長大，即1歲半左右。黑熊在野外可以活到長達(dá)30年，在專門的保護(hù)區(qū)中甚至能活得更長。

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1hibernate

v.冬眠，蟄伏參考例句：Bearsoftenhibernateincaves.熊常在山洞里冬眠。Somewarm-bloodedanimalsdonotneedtohibernate.一些溫血?jiǎng)游锊恍枰摺?moths

n.蛾(moth的名詞復(fù)數(shù))參考例句：Themothshaveeatenholesinmywoolcoat.蛀蟲將我的羊毛衫蛀蝕了幾個(gè)小洞。來自《簡明英漢詞典》Themothstappedandblurredatthewindowscreen.飛蛾在窗簾上跳來跳去，弄上了許多污點(diǎn)。來自《現(xiàn)代英漢綜合大詞典》3remains

n.剩余物，殘留物；遺體，遺跡參考例句：Heatetheremainsoffoodhungrily.他狼吞虎咽地吃剩余的食物。Theremainsofthemealwerefedtothedog.殘羹剩飯喂狗了。4dense

a.密集的，稠密的，濃密的；密度大的參考例句：Thegeneralambushedhistroopsinthedensewoods.將軍把部隊(duì)埋伏在濃密的樹林里。Thepathwascompletelycoveredbythedensefoliage.小路被樹葉厚厚地蓋了一層。5thickets

n.灌木叢(thicket的名詞復(fù)數(shù))；叢狀物參考例句：Smalltreesbecamethinlyscatteredamonglessdensethickets.小樹稀稀朗朗地立在樹林里。來自辭典例句Theentiresurfaceiscoveredwithdensethickets.所有的地面蓋滿了密密層層的灌木叢。來自辭典例句6cubs

n.幼小的獸，不懂規(guī)矩的年輕人(cub的名詞復(fù)數(shù))參考例句：alionessguardinghercubs守護(hù)幼崽的母獅Lioncubsdependontheirmothertofeedthem.獅子的幼仔依靠母獅喂養(yǎng)。來自《簡明英漢詞典》7gestation

n.懷孕；醞釀參考例句：Thegestationperiodcanbeanythingbetween95and150days.妊娠期從95天至150天不等。Thisfilmwastwoyearsingestation.這部電影醞釀了兩年。8fully

adv.完全地，全部地，徹底地；充分地參考例句：Thedoctoraskedmetobreathein,thentobreatheoutfully.醫(yī)生讓我先吸氣，然后全部呼出。Theysoonbecamefullyintegratedintothelocalcommunity.他們很快就完全融入了當(dāng)?shù)厝说娜ψ?。Coal-firedpowerplantsCoal-firedpowerplantsTheinventionoftheincandescent1lightbulbbyThomasA.Edisonin1879createdademandforacheap,readilyavailablefuelwithwhichtogeneratelargeamountsofelectricpower.Coalseemedtofitthebill,anditfueledtheearliestpowerstations.(whichweresetupattheendofthenineteenthcenturybyEdisonhimself).Asmorepowerplantswereconstructedthroughoutthecountry,therelianceoncoalincreasedthroughoutthecountry,therelianceoncoalincreased.SincetheFirstWorldWar,coal-firedpowerplantshadacombinedintheUnitedStateseachyear.In1986suchplantshadacombinedgeneratingcapacityof289,000megawattsandconsumed83percentofthenearly900milliontonsofcoalminedinthecountrythatyear.Giventheuncertainty2inthefuturegrowthofthenearly900milliontonsofcoalminedinthecountrythatyear.Giventheuncertaintyinthefuturegrowthofnuclearpowerandinthesupplyofoilandnaturalgas,coal-firedpowerplantscouldwellprovideupto70percentoftheelectricpowerintheUnitedStatesbytheendofthecentury.Yet,inspiteofthefactthatcoalhaslongbeenasourceofelectricityandmayremainonformanyyears(coalrepresentsabout80percentofUnitedStatesfossil-fuelreserves),ithasactuallyneverbeenthemostdesirablefossilfuelforpowerplants.Coalcontainslessenergyperunitofweightthanweightthannaturalgasoroil;itisdifficulttotransport,anditisassociatedwithahostofenvironmentalissues,amongthemacidrain.Sincethelate1960’sproblemsofemission3controlandwastedisposalhavesharplyreducedtheappealofcoal-firedpowerplants.Thecostofamelioratingtheseenvironmentproblemsalongwiththerisingcostofbuildingafacilityaslargeandcomplexasacoal-firedpowerplant,havealsomadesuchplantslessattractivefromapurely4economicperspective.Changesinthetechnological5baseofcoal-firedpowerplantscouldrestoretheirattractiveness,however.Whereassomeofthesechangesareintendedmainlytoincreasetheproductivityofexistingplants,completelynewtechnologiesforburningcoalcleanlyarealsobeingdeveloped.火力發(fā)電廠托馬斯?愛迪生1879年發(fā)明的白熾燈導(dǎo)致對(duì)便宜、易得、可生產(chǎn)大量電能的燃料的需求。煤似乎符合這個(gè)要求，并成為第一批電廠的燃料(正是愛迪生本人在19世紀(jì)末建造了第一批電廠)。全國到處興建電廠時(shí)，對(duì)煤的依賴加深了。自第一次世界大戰(zhàn)以來，美國每年約有一半的電力是以煤為燃料的電廠提供的。1986年這些電廠的總發(fā)電能力達(dá)到28，900千瓦并且消耗了當(dāng)年全國開采的九億噸煤的83%?？紤]到核能發(fā)展以及石油、天然氣供應(yīng)中的不確定因素，到本世紀(jì)末，火力發(fā)電廠仍可能為美國提供多達(dá)70%的電力。然而，盡管煤長期以來一直是電力的原料之一并且可能會(huì)繼續(xù)如此(煤占美國化石燃料儲(chǔ)量的80%)，它卻不是電廠的理想燃料。煤的單位能量含量低于石油和天然氣，而且會(huì)導(dǎo)致包括酸雨在內(nèi)的一系列環(huán)境問題。從1960年以來，排放控制和垃圾處理的問題極大地削弱了燃煤電廠的魅力。由于減輕這些環(huán)境問題需要大量資金，而且建造龐大復(fù)雜的燃煤電廠的費(fèi)用不斷上漲，也使得這些電廠從經(jīng)濟(jì)角度上不具備吸引力。改變火力發(fā)電廠的基礎(chǔ)技術(shù)卻可能恢復(fù)它們的吸引力。雖然某些技術(shù)改進(jìn)是漸進(jìn)的，其目的只是提高現(xiàn)有電廠的生產(chǎn)率，但人們正在開發(fā)全新的清潔燃煤的技術(shù)。點(diǎn)擊收聽單詞發(fā)音

1incandescent

adj.遇熱發(fā)光的，白熾的，感情強(qiáng)烈的參考例句：TheincandescentlampweuseindailylifewasinventedbyEdison.我們?nèi)粘Ｉ钪杏玫陌谉霟?，是愛迪生發(fā)明的。Theincandescentqualityofhiswordsilluminatedthecourageofhiscountrymen.他熾熱的語言點(diǎn)燃了他本國同胞的勇氣。2uncertainty

n.易變，靠不住，不確知，不確定的事物參考例句：Hercommentswilladdtotheuncertaintyofthesituation.她的批評(píng)將會(huì)使局勢更加不穩(wěn)定。Aftersixweeksofuncertainty,thestrainwasbeginningtotakeitstoll.6個(gè)星期的忐忑不安后，壓力開始產(chǎn)生影響了。3emission

n.發(fā)出物，散發(fā)物；發(fā)出，散發(fā)參考例句：Rigorousmeasureswillbetakentoreducethetotalpollutantemission.采取嚴(yán)格有力措施，降低污染物排放總量。Finally,thewaytoeffectivelycontrolparticulateemissionispointedout.最后，指出有效降低顆粒排放的方向。4purely

adv.純粹地，完全地參考例句：Ihelpedhimpurelyandsimplyoutoffriendship.我?guī)退兇馐浅鲇谟亚椤hisdisprovesthetheorythatchildrenarepurelyimitative.這證明認(rèn)為兒童只會(huì)單純地模仿的理論是站不住腳的。5technological

adj.技術(shù)的；工藝的參考例句：Asuccessfulcompanymustkeepupwiththepaceoftechnologicalchange.一家成功的公司必須得跟上技術(shù)變革的步伐。Today,thepaceoflifeisincreasingwithtechnologicaladvancements.當(dāng)今，隨著科技進(jìn)步，生活節(jié)奏不斷增快。StatisticsStatisticsThereweretwowidelydivergentinfluencesontheearlydevelopmentofstatistical1methods.Statisticshadamotherwhowasdedicated2tokeepingorderlyrecordsofgovernmentunits(statesandstatisticscomefromthesameLatinrootstatus)andagentlemanlygambling3fatherwhoreliedonmathematicstoincreasehisskillatplayingtheodds4ingamesofchance.Theinfluenceofthemotherontheoffspring,statistics,isrepresentedbycounting,measuring,describing,tabulating5,ordering,andthetakingofcensuses—allofwhichledtomoderndescriptivestatistics.Fromtheinfluenceofthefathercamemoderninferentialstatistics,whichisbasedsquarelyontheoriesofprobability.Describingcollectionsinvolvestabulating,depicting6anddescribingcollectionsofdata.Thesedatamaybequantitative7suchasmeasuresofheight,intelligenceorgradelevel------variablesthatarecharacterizedbyanunderlying8continuum---orthedatamayrepresentqualitative9variables,suchassex,collegemajororpersonalitytype.Largemassesofdatamustgenerallyundergoaprocessofsummarizationorreductionbeforetheyarecomprehensible.Descriptivestatisticsisatoolfordescribingorsummarizingorreducingtocomprehensibleformthepropertiesofanotherwiseunwieldymassofdata.Inferentialstatisticsisaformalizedbodyofmethodsforsolvinganotherclassofproblemsthatpresentgreatofproblemscharacteristicallyinvolvesattemptstomakepredictionsusingasampleofobservations.Forexample,aschoolsuperintendent10wishestodeterminetheproportionofchildreninalargeschoolsystemwhocometoschoolwithoutbreakfast,havebeenvaccinated11forflu,orwhatever.Havingalittleknowledgeofstatistics,thesuperintendentwouldknowthatitisunnecessaryandinefficient12toquestioneachchild:theproportionforthesampleofasfewas100children.Thus,thepurposeofinferentialstatisticsistopredictorestimatecharacteristicsofapopulationfromaknowledgeofthecharacteristicsofonlyasampleofthepopulation.統(tǒng)計(jì)學(xué)統(tǒng)計(jì)方法的早期發(fā)展受到兩種截然不同的影響。統(tǒng)計(jì)學(xué)有一個(gè)"母親"，她致力于井井有條地記錄政府機(jī)構(gòu)的文件(國家和統(tǒng)計(jì)學(xué)這兩個(gè)詞源于同一個(gè)拉丁語詞根，status)，還有一個(gè)有紳士般的賭博"父親"，他依靠數(shù)學(xué)來提高賭技，以便在幾率的游戲中取勝。"母親"對(duì)其子女統(tǒng)計(jì)學(xué)的影響表現(xiàn)在計(jì)數(shù)、測量、描述、制表、歸類和人口普查。所有這些導(dǎo)致了現(xiàn)代描述統(tǒng)計(jì)學(xué)的誕生。由于"父親"的影響則產(chǎn)生了完全基于概率論原理的現(xiàn)代推理統(tǒng)計(jì)學(xué)。描述統(tǒng)計(jì)學(xué)涉及對(duì)所收集數(shù)據(jù)的制表、制圖和描述。這些數(shù)據(jù)可以是數(shù)量性的數(shù)據(jù)，如高度、智商、或者是層級(jí)性的數(shù)據(jù)--具有連續(xù)性的變量--或數(shù)據(jù)也可以代表性質(zhì)變量，如性別、大學(xué)專業(yè)或性格類型等等。數(shù)量龐大的數(shù)據(jù)通常必須經(jīng)過概括或刪減的程序才能為人所理解。描述統(tǒng)計(jì)學(xué)就是這樣一個(gè)工具，它對(duì)極其龐雜的數(shù)據(jù)進(jìn)行描述、概括或刪減，使其變成能為人理解的東西。推理統(tǒng)計(jì)學(xué)是一套已定形了的方法體系，它解決的是光憑人腦極難解決的另一類問題。這類問題的顯著特點(diǎn)是試圖通過取樣調(diào)查來作出預(yù)測。例如，有一位教育督察想知道在一個(gè)龐大的學(xué)校系統(tǒng)中，不吃早飯就上學(xué)的學(xué)生、已經(jīng)做過防感冒免疫的學(xué)生，或其它任何類型的學(xué)生占多大比例。若具備一些統(tǒng)計(jì)學(xué)的知識(shí)，這位督察應(yīng)明白，詢問每個(gè)孩子是沒有必要而且沒有效率的，只要用100個(gè)孩子為樣本，他就可以相當(dāng)精確地得出這些孩子占整個(gè)學(xué)區(qū)的比例了。因此，推理統(tǒng)計(jì)學(xué)的目的就是通過了解一個(gè)群體中一些樣本的特性，從而對(duì)整個(gè)群體的特性進(jìn)行推測和估算。

點(diǎn)擊收聽單詞發(fā)音

1statistical

adj.統(tǒng)計(jì)的，統(tǒng)計(jì)學(xué)的參考例句：Heshowedthepricefluctuationsinastatisticaltable.他用統(tǒng)計(jì)表顯示價(jià)格的波動(dòng)。They'remakingdetailedstatisticalanalysis.他們正在做具體的統(tǒng)計(jì)分析。2dedicated

adj.一心一意的；獻(xiàn)身的；熱誠的參考例句：Hededicatedhislifetothecauseofeducation.他獻(xiàn)身于教育事業(yè)。Hiswholeenergiesarededicatedtoimprovethedesign.他的全部精力都放在改進(jìn)這項(xiàng)設(shè)計(jì)上了。3gambling

n.賭博；投機(jī)參考例句：Theyhavewonalotofmoneythroughgambling.他們賭博贏了很多錢。Themenhavebeengamblingawayallnight.那些人賭了整整一夜。4odds

n.讓步，機(jī)率，可能性，比率；勝