Scientific American Magazine 1993年01月 .pdf

《Scientific American Magazine 1993年01月 .pdf》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

1、JANUARY1993$3.95TheturbulentbirthoftheMilkyWay.Lemurs:aglimpseatourevolutionarypast.Fromquantumdotstodesigneratoms.Stickysugars:carbohydratesmediatemanycellularinteractions,suchasinfectionandinßammation.Copyright1992ScientificAmerican,Inc.January1993Volume268Number164CoralBleachin

2、gBarbaraE.BrownandJohnC.OgdenExtensiveareasofthesubtlycoloredcoralreefsthatgirdtropicalshoreshavebeenturningadazzlingwhite;somestretchesoftheaÝectedcoralhaveevendied.Bleachingmaybeacallofdistressfromthesecomplexandhighlyproduc-tiveecosystems,usuallyemittedwhentheyexperienceabnorma

3、llyhighseawatertemperatures.Dobleachedreefssignalglobalwarming?72HowtheMilkyWayFormedSidneyvandenBerghandJamesE.HesserFormorethanadecade,astronomershavebelievedourgalaxyandotherslikeitformedfromtherapidcollapseofanenormouscloudofhydrogenandheliumgas.Observationnolongerentirelysupp

4、ortsthissimplemodel.TheMilkyWaycameintobeingundertheinßuenceofexplodingstars,itsownrotationandper-hapsapropensitytocaptureandgobbleupotherprotogalaxies.82CarbohydratesinCellRecognitionNathanSharonandHalinaLisCarbohydratemoleculesarethechemicalbraillethatenablescellstorecognizeandr

5、espondtooneanother.Withthem,bacteriaidentifytheirhosts,andthecellsoftheimmunesystemsingleoutdiseasedtissue.Carbohydratesalsodirectcellularorganizationinembryos.Naturehasselectedthemforsuchcodingbe-causetheyformthelargestnumberofcombinationsfromafewcomponents.90TheEarliestHistoryof

6、theEarthDerekYorkTheearthisextremelygoodatdestroyingevidenceofitspast.Themassivetecton-icplatesregularlyplungeunderoneanother,returningtheoceanßoortomoltenoblivionandcausingcontinentstocollide.Yetincreasinglysophisticatedradioac-tivedatingtechniquesareenablinggeologiststoprythehis

7、toryoftheplanetÕsÞrstbillionandahalfyearsfromancient,previouslytaciturncontinentalrock.110MadagascarÕsLemursIanTattersallTheproperstudyofhumansisthelemur.Ofalllivingcreatures,nonemorecloselyresemblestheancestorfromwhichhumansandthegreatapesbranched50millionyearsago.ButthelemursÕdi

8、verseMadagascanhabitatsaredisappe