ASTM A90／A90M − 13镀锌和镀锌合金钢铁制品镀层重量的试验方法

Designation:A90/A90M−13StandardTestMethodforWeight[Mass]ofCoatingonIronandSteelArticleswithZincorZinc-AlloyCoatings1ThisstandardisissuedunderthefixeddesignationA90/A90M;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.ThisstandardhasbeenapprovedforusebyagenciesoftheDepartmentofDefense.1.Scope*1.1Thistestmethodcoversproceduresfordeterminingtheweight[mass]ofcoatingonironorsteelsheet,wire,andotherarticlesinwhichthecoatingiszincorazincalloy,suchaszinc-5%aluminum(includingzinc-5%aluminum-mischmetalandzinc-5%aluminum-0.1%magnesium),zinc-aluminum-magnesium(includingzinc-5to9%aluminum-magnesiumandzinc-9to13%aluminum-magnesium)or55%aluminum-zinc.Inthebodyofthistestmethod,referencetozinccoatingshallbeinterpretedtoalsoincludezincalloycoatingexceptwherespecificallystatedotherwise.1.2Thefinalresultsdeterminedbythistestmethodshallbeexpressedininch-poundunitsorSIunits,dependingontheunitsusedinthematerialspecificationtowhichtheresultsaretobecompared.Certainportionsoftheprocedureinvolvingdeterminationofspecimenweight[mass]havetraditionallybeenperformedinSIunits,andcorrespondinginch-poundunitsarenotincluded.1.3Forsheetproducts,thefinalresultsareexpressedaseithercoatingweight[mass]totalbothsides,orcoatingweight[mass]separatelyoneachside,dependingonthespecifiedrequirements.1.4Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.Forspecifichazardsstatementssee5.1.2.ReferencedDocuments2.1ASTMStandards:2A653/A653MSpecificationforSteelSheet,Zinc-Coated(Galvanized)orZinc-IronAlloy-Coated(Galvannealed)bytheHot-DipProcessA792/A792MSpecificationforSteelSheet,55%Aluminum-ZincAlloy-CoatedbytheHot-DipProcessA875/A875MSpecificationforSteelSheet,Zinc-5%Alu-minumAlloy-CoatedbytheHot-DipProcessA1046/A1046MSpecificationforSteelSheet,Zinc-Aluminum-MagnesiumAlloy-CoatedbytheHot-DipPro-cessA1057/A1057MSpecificationforSteel,StructuralTubing,ColdFormed,Welded,Carbon,Zinc-Coated(Galvanized)bytheHot-DipProcessA1063/A1063MSpecificationforSteelSheet,Twin-RollCast,Zinc-Coated(Galvanized)bytheHot-DipProcessA1079SpecificationforSteelSheet,ComplexPhase(CP),DualPhase(DP)andTransformationInducedPlasticity(TRIP),Zinc-Coated(Galvanized)orZinc-IronAlloy-Coated(Galvannealed)bytheHot-DipProcessD1193SpecificationforReagentWaterE29PracticeforUsingSignificantDigitsinTestDatatoDetermineConformancewithSpecifications3.SignificanceandUse3.1Thistestmethodprovidesastandardmethodfordeter-miningtheweight[mass]ofcoatingforcomparisonwithspecificationrequirements.Acoatingofzinconironorsteelarticlesprovidesprotectionagainstcorrosion.Astheprotectionisprovidedbysacrificiallossofzinc,thedegreeofprotectionisproportionaltotheweight[mass]ofzinccoating.Specifi-cationsforzinc-coatedarticlesfrequentlyprovidefordifferentclassesofcoatingsothatthepurchasercanselectthecoatingweight[mass]mostsuitabletohisneeds.1ThistestmethodisunderthejurisdictionofASTMCommitteeA05onMetallic-CoatedIronandSteelProductsandisthedirectresponsibilityofSubcommitteeA05.07onMethodsofTesting.CurrenteditionapprovedApril1,2013.PublishedApril2013.Originallyapprovedin1923.Lastpreviouseditionapprovedin2011asA90/A90M-11.DOI:10.1520/A0090_A0090M-13.2ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.ForAnnualBookofASTMStandardsvolumeinformation,refertothestandard’sDocumentSummarypageontheASTMwebsite.*ASummaryofChangessectionappearsattheendofthisstandardCopyright©ASTMInternational,100BarrHarborDrive,POBoxC700,WestConshohocken,PA19428-2959.UnitedStates1CopyrightbyASTMInt'l(allrightsreserved);FriAug2303:21:46EDT2013Downloaded/printedbyShanghaiJiaotongUniversitypursuanttoLicenseAgreement.Nofurtherreproductionsauthorized.4.Reagents4.1PurityofReagents—Reagentgradechemicalsshallbeusedinalltests.Unlessotherwiseindicated,itisintendedthatallreagentsshallconformtothespecificationsoftheCommit-teeonAnalyticalReagentsoftheAmericanChemicalSociety,wheresuchspecificationsareavailable.3Othergradesmaybeused,provideditisfirstascertainedthatthereagentisofsufficientlyhighpuritytopermititsusewithoutlesseningtheaccuracyofthedetermination.4.2PurityofWater—Waterusedtopreparechemicalsolu-tionsshallbereagentwaterasdefinedbyTypeIVofSpecificationD1193.4.3AntimonyTrichlorideSolution—Dissolve20gofSb2O3or32gofSbCl3in1000mLofHCl(spgr1.18to1.19).4.4HydrochloricAcid(spgr1.18to1.19)—Concentratedhydrochloricacid(HCl).4.5HydrochloricAcid—AntimonyTrichlorideSolution—Add5mLofantimonytrichloridesolutionto100mLofHCl(spgr1.18to1.19).4.6HydrochloricAcid(1+1)—Mix500mLofHCl(spgr1.18to1.19)with500mLofreagentwaterandcooltoroomtemperature.4.7SulfuricAcid(25+75)—Mix250mLofH2SO4(spgr1.84)with750mLofreagentwaterandcooltoroomtemperature.NOTE1—Itisadvisabletouseaninhibitorwithacidsolution(forexample,HexamethylamineTetramineorsimilar)attheconcentrationlevelaccordingtothemanufacturer’srecommendationstopreventattackofthesubstrate.5.Hazards5.1Warning—Smallamountsofthepoisonousgasstibine(SbH3)maybeevolvedduringthestrippingprocessusingthehydrochloricacid-antimonytrichloridemethod.Hydrochloricacidfumesarepresent,andhydrogengasisevolvedinthestrippingprocess.Therefore,thetestshouldbeperformedunderconditionsofadequateventilation.Afumehoodisrecommendedforlargenumbersofsamplesorwherethetestistobecarriedoutfrequentlyoverextendedperiodsoftime.5.2Warning—Mixingofsulfuricacidwithwatercouldresultinsevereinjuriesifnotproperlydone.Mixingmustbedonebyslowlyaddingsulfuricacidtowaterduetotheheatgeneratedandpossiblesplashing.Undernocircumstancesshouldthewaterbeaddedtotheacid.Themixingshouldbeperformedunderanacidfumehood.6.Sampling6.1Zinc-CoatedSheets—Samplesforweight[mass]ofcoatingdeterminationshallbesecuredinaccordancewithSpecificationsA653/A653M,A792/A792M,A875/A875M,A1046/A1046M,A1057/A1057M,A1063/A1063M,orA1079dependingonthetypeofcoating.NOTE2—Forconvenienceincalculatingtestresultsininch-poundunits,thespecimenshouldhaveanareaof5.08in.2ofsheet(2.2560.01-in.squareor2.5460.01in.indiameter).Theweight[mass]ofcoatingingramsonaspecimenofthatareaisnumericallyequaltotheweight[mass]ofcoatinginouncespersquarefootofsheet.Forresultstobereportedinmetricunits,thespecimenshouldhaveanareaof3330mm2ofsheet(57.760.1-mmsquareor65.160.1mmindiameter).6.2Zinc-CoatedWire—Samplesshallbesecuredasdesig-natedintheappropriatespecification.Thespecimenofwiremaybeofanylengthover12in.[305mm],butpreferablyabout24in.[609mm].Whereacontinuouslengthisnotavailable,shorterlengthstotalingover12in.[300mm],butpreferablyabout24in.[600mm],shallbeused.Sincethedensityofthesteelisknown0.283lb/in.3[7830kg/m3],itisnotnecessarytouseaspecificlengthofspecimen.6.3Zinc-CoatedArticlesOtherThanSheetorWire—Samplesforweight[mass]ofcoatingdeterminationshallbesecuredasdesignatedintheappropriatespecification.Exceptasotherwiseprovided,thespecimensshouldhaveaminimumareaof3in.2(2000mm2)ofzinc-coatedsurface.Forverysmallitems,severalpiecesmayhavetobestrippedtoobtaintheminimumarea.6.3.1Inthecaseofthreadedarticles,suchasboltsandscrews,thedeterminationshallbemadeonaportionofthearticlesthatdoesnotincludeanythread.7.Procedure7.1Stripthezinccoatingfromthespecimensbyusingoneofthefollowingmethods:hydrochloricacid(1+1),hydro-chloricacid-antimonytrichloridesolution,orsulfuricacid(25+75).Forzincalloycoatingscontaininglessthan90%zinc,thestrippingshallbedoneusinghydrochloricacid(1+1)orsulfuricacid(25+75).7.2Cleanthespecimensbywashingwithsolventnaphthaorothersuitablesolvent,thenrinsewithalcohol,anddrythor-oughly.7.3Determinetheweight[mass]ofthespecimensindividu-allytothenearest0.01g,exceptforarticlesotherthansheetorwirewithaspecimenweight[mass]greaterthan125g,determinetheweight[mass]toatleastthenearest0.1g.Afterdeterminingtheweight[mass],immerseeachspecimensinglyinthestrippingsolutionandallowtoremainuntiltheviolentevolutionofhydrogenhasceased,andonlyafewbubblesarebeingevolved.Thisrequiresabout15to30s,exceptinthecaseofsherardizedcoatings,whichrequireasomewhatlongertime.Thesamesolutionmaybeusedrepeatedlyuntilthetimerequiredforstrippingbecomesinconvenientlylong.Thetem-peratureofthestrippingsolutionshallatnotimeexceed100°F[38°C].Afterstripping,washthespecimensbyscrubbingthemunderrunningwater,dipinhotwater,andwipeorblowdry.Determinetheweight[mass]ofthespecimensagain,tothesameprecisionasintheinitialdetermination.7.4SheetSpecimens—Whenmeasuringthetotalcoatingweight[mass]onbothsides,orthesinglesidecoatingweight[mass]oneachside,determinetheareaofsheet(onesurface)3“ReagentChemicals,AmericanChemicalSocietySpecifications,”Am.Chemi-calSoc.,Washington,DC.ForsuggestionsonthetestingofreagentsnotlistedbytheAmericanChemicalSociety,see“AnalarStandardsforLaboratoryU.K.Chemicals,”BDHLtd.,Poole,Dorset,andthe“UnitedStatesPharmacopeia.”A90/A90M−132CopyrightbyASTMInt'l(allrightsreserved);FriAug2303:21:46EDT2013Downloaded/printedbyShanghaiJiaotongUniversitypursuanttoLicenseAgreement.Nofurtherreproductionsauthorized.tothenearest0.01in.2[5mm2].IfspecimenswerepreparedtothedimensionsasprovidedinNote2,theyshallbepresumedtohaveanareaof5.08in.2[3330mm2].Whenitisnotpossibletodeterminetheareaaccurately,asinspecimensfromcorru-gatedsheets,thethicknessofthestrippedsheetshallbedeterminedtothenearest0.001in.[0.01mm].7.4.1Whendeterminingthecoatingweight[mass]ononesideofsheetmaterial,usetheproceduredescribedin7.3,exceptusea“stop-off”toprotectonesidefromthestrippingmedium.Acid-resistantpaintsorlacquers,acid-resistanttape,ormechanicaldevicesfastenedtothetestspecimenareexamplesofcommonlyused“stop-off”materials.Applythe“stop-off”tothespecimenaftertheinitialdeterminationofweight[mass]andremovebeforetheseconddeterminationofweight[mass].Becauseofthepossibilityofmoistureabsorp-tionduringthestrippingprocess,the“stop-off”mustnotbeonthespecimenduringeitherweight[mass]determinations.Determinethecoatingweight[mass]onthesecondsidesubsequentlywithouta“stop-off”onthefirstside.7.5WireSpecimens—Determinethediameterofthestrippedwiretothenearest0.001in.[0.01mm]bytakingtheaverageoftwomeasurementsatrightanglestoeachother.7.6SpecimensOtherThanSheetorWire—Determinethetotalcoatedareaoftheoriginalspecimentothenearest0.01in.2[5mm2].Alternatively,forspecimensofuniformthicknessofbasemetal,suchasapieceofplateorpipe,determinetheaveragethicknessofthestrippedspecimentothenearest0.001in.[0.01mm].8.Calculation8.1Zinc-CoatedSheet:8.1.1ResultsinInch-PoundUnits:8.1.1.1Whentheareaofonesurfaceofthesheetisdetermined,calculatetheweight[mass]ofcoatingasfollows:C5@~W12W2!/A#3K(1)where:C=weight[mass]ofcoating,oz/ft2ofsheet,W1=originalweight[mass]ofspecimen,g,W2=weight[mass]ofstrippedspecimen,g,A=areaofonesurfaceofthesheet,in.2ormm2,and,K=aconstant=5.08whenAisinin.2,or=3.28×103whenAisinmm2.NOTE3—IfthespecimenwaspreparedtothedimensionsasprovidedinNote2,havinganareaof5.08in.2,thelossofweight[mass]ingramsisnumericallyequaltotheweight[mass]ofcoatinginouncespersquarefootofsheet.8.1.1.2Whenitisnotpossibletosecureaspecimenofmeasurablearea,calculatetheweight[mass]ofcoatingasfollows:C5@~W12W2!/W2#3T3K(2)where:C=weight[mass]ofcoating,oz/ft2ofsheet,W1=originalweight[mass]ofspecimen,g,W2=weight[mass]ofstrippedspecimen,g,T=thicknessofstrippedsheet,in.ormm,andK=aconstant=652whenTisinin.,or=25.7whenTisinmm.8.1.2ResultsinMetricUnits:8.1.2.1Whentheareaofsheetisdetermined,calculatetheweight[mass]ofcoatingasfollows:C5@~W12W2!/A#3K(3)where:C=weight[mass]ofcoating,g/m2ofsheet,W1=originalweight[mass]ofspecimen,g,W2=weight[mass]ofstrippedspecimen,g,A=areaofonesurfaceofthesheet,in.2ormm2,andK=aconstant=1.55×103whenAisinin.2,or=1×106whenAisinmm2.NOTE4—IfthespecimenwaspreparedtothedimensionsasprovidedinNote2,havinganareaof3330mm2ofsheet,thefactorK/Aisapproximately300,whichmaybeusedinthecalculation.8.1.2.2Whenitisnotpossibletoobtainaspecimenofmeasurablearea,calculatetheweight[mass]ofcoatingasfollows:C5@~W12W2!/W2#3T3K(4)where:C=weight[mass]ofcoating,g/m2ofsheetW1=originalweight[mass]ofthespecimen,g,W2=weight[mass]ofthestrippedspecimen,g,T=thicknessofstrippedsheet,in.ormm,andK=aconstant=1.99×105whenTisinin.,or=7.83×103whenTisinmm.8.2Zinc-CoatedWire:8.2.1ResultsinInch-PoundUnits:8.2.1.1Calculatetheweight[mass]ofzinccoatingasfollows:C5@~W12W2!/W2#3D3M(5)where:C=weight[mass]ofcoating,oz/ft2ofstrippedwiresurface,W1=originalweight[mass]ofspecimen,g,W2=weight[mass]ofstrippedspecimen,g,D=diameterofstrippedwire,in.ormm,andM=aconstant=163whenDisinin.,or=6.42whenDisinmm.8.2.2ResultsinMetricUnits:8.2.2.1Calculatetheweight[mass]ofzinccoatingasfollows:C5@~W12W2!/W2#3D3M(6)where:C=weight[mass]ofcoating,g/m2ofstrippedwiresurface,W1=originalweight[mass]ofspecimen,g,W2=weight[mass]ofstrippedspecimen,g,D=diameterofstrippedwire,in.ormm,andM=aconstant=4.97×104whenDisinin.,or=1.96×103whenDisinmm.8.3Zinc-CoatedArticlesOtherThanSheetorWire:8.3.1ResultsinInch-PoundUnits:A90/A90M−133CopyrightbyASTMInt'l(allrightsreserved);FriAug2303:21:46EDT2013Downloaded/printedbyShanghaiJiaotongUniversitypursuanttoLicenseAgreement.Nofurtherreproductionsauthorized.8.3.1.1Calculatetheweight[mass]ofcoatingasfollows:C5@~W12W2!/A#3N(7)where:C=weight[mass]ofcoating,oz/ft2ofsurface,W1=originalweight[mass]ofspecimen,g,W2=weight[mass]ofstrippedspecimen,g,A=coatedareaoforiginalspecimen,in.2ormm2,andN=aconstant=5.08whenAisinin.2,or=3.28×103whenAisinmm2.8.3.1.2Ifthespecimenhasauniformthicknessofbasemetal,calculatetheweight[mass]ofcoatingasfollows:C5@~W12W2!/W2#3G3Z(8)where:C=weight[mass]ofcoating,oz/ft2ofsurface,W1=originalweight[mass]ofspecimen,g,W2=weight[mass]ofstrippedspecimen,g,G=thicknessofstrippedspecimen,in.ormm,andZ=aconstant=326whenGisinin.,or12.8whenGisinmm.8.3.2ResultsinMetricUnits:8.3.2.1Calculatetheweight[mass]ofzinccoatingasfollows:C5@~W12W2!/A#3N(9)where:C=weight[mass]ofcoating,g/m2ofsurface,W1=originalweight[mass]ofspecimen,g,W2=weight[mass]ofstrippedspecimen,g,A=coatedareaoforiginalspecimen,in.2ormm2,andN=aconstant=1.55×103whenAisinin.2,or=1×106whenAisinmm2.8.3.2.2Ifthespecimenhasauniformthicknessofbasemetal,calculatetheweight[mass]ofcoatingasfollows:C5@~W12W2!/W2#3G3Z(10)where:C=weight[mass]ofcoating,g/m2ofsurface,W1=originalweight[mass]ofspecimen,g,W2=weight[mass]ofstrippedspecimen,g,G=thicknessofstrippedspecimen,in.ormm,andZ=aconstant=9.95×104whenGisinin.,or=3.92×103whenGisinmm.9.Report9.1Weight[mass]ofcoatingonzinc-coatedsheetisex-pressedinweight[mass]perunitareaofsheet,andiseitherthesumoftheweights[masses]ofcoatingonbothsidesofthesheet,orsinglesideweight[mass]oneachofthetwosides.Weights[masses]ofcoatingoneachsideofthesheetarenotnecessarilyequal,evenwhenbothsidesareexposedtothemoltenmetalorplatingsolutionsimultaneously.Coatingweights[masses]onallzinc-coatedarticlesotherthansheetsareexpressedinweight[mass]perunitareaofsurface.9.2Reporttheweight[mass]ofzinccoatingtothenearest0.01oz/ft2whenreportingininch-poundunits.9.3Reporttheweight[mass]ofzinccoatingtothenearest1g/m2whenreportinginmetricunits.9.4Whentheweight[mass]ofcoatingofanumberofspecimensistobeaveragedtodetermineconformancewithaspecificationlimit,theaveragevalueshallbereportedtotheprecisiondescribedin9.2and9.3inaccordancewiththeRoundingMethodofPracticeE29.10.PrecisionandBias10.1Theprecisionofthistestmethodisbasedonaninterlaboratorystudyconductedin2006.Eachoftenlaborato-riestestedthreereplicatesoftwodifferentmaterials.4Datawasrecordedininch-poundunitsonlyandshouldnotbeconsideredmetricequivalents.SeeTable1forastatisticalsummaryofthetestresults.10.1.1Repeatability—Twotestresultsobtainedwithinonelaboratoryshallbejudgednotequivalentiftheydifferbymorethanthe“r”valueforthatmaterial;“r”istheintervalrepresentingthecriticaldifferencebetweentwotestresultsforthesamematerial,obtainedbythesameoperatorusingthesameequipmentonthesamedayinthesamelaboratory.10.1.2Reproducibility—Twotestresultsshallbejudgednotequivalentiftheydifferbymorethanthe“R”valueforthatmaterial;“R”istheintervalrepresentingthedifferencebe-tweentwotestresultsforthesamematerial,obtainedbydifferentoperatorsusingdifferentequipmentindifferentlabo-ratories.10.1.3Anyjudgmentinaccordancewiththesetwostate-mentswouldhaveanapproximate95%probabilityofbeingcorrect.10.2Bias—Atthetimeofthestudy,therewasnoacceptedreferencematerialsuitablefordeterminingthebiasforthistestmethod,thereforenostatementonbiasisbeingmade.10.3Theprecisionstatementwasdeterminedthroughsta-tisticalexaminationofthreeresults,fromtenlaboratories,ontwomaterials.11.Keywords11.155%aluminum-zincalloycoating;coatingweight[mass];steelsheet;steelwire;zincalloycoatings;zinccoating;4SupportingdatahavebeenfiledatASTMInternationalHeadquartersandmaybeobtainedbyrequestingResearchReportRR:A05-1003.TABLE1WeightMassCoating(inoz.ft2)NOTE1—Srmeansthestandarddeviationofr(repeatability).SRmeansthestandarddeviationforR(reproducibility).Materialx¯Sx¯SrSRrRHotDippedZinc-CoatedSamples1.1007800.0218950.0153330.0252220.0429330.070621ElectrolyticZinc-CoatedSamples0.4032210.0087900.0083780.0111380.0234570.031187A90/A90M−134CopyrightbyASTMInt'l(allrightsreserved);FriAug2303:21:46EDT2013Downloaded/printedbyShanghaiJiaotongUniversitypursuanttoLicenseAgreement.Nofurtherreproductionsauthorized.zinc-5%aluminumalloycoating;zinc-5%aluminum-0.1%magnesiumalloycoating;zinc-5%aluminum-mischmetalal-loycoating;zinc-5to9%aluminum-magnesiumalloycoating;zinc-9to13%aluminum-magnesiumalloycoatingSUMMARYOFCHANGESCommitteeA05hasidentifiedthelocationofselectedchangestothisstandardsincethelastissue(A90/A90M-11)thatmayimpacttheuseofthisstandard.(April1,2013)(1)AddedreferencestoA1057/A1057MandA1079in2.1and6.1.ASTMInternationaltakesnopositionrespectingthevalidityofanypatentrightsassertedinconnectionwithanyitemmentionedinthisstandard.Usersofthisstandardareexpresslyadvisedthatdeterminationofthevalidityofanysuchpatentrights,andtheriskofinfringementofsuchrights,areentirelytheirownresponsibility.Thisstandardissubjecttorevisionatanytimebytheresponsibletechnicalcommitteeandmustbereviewedeveryfiveyearsandifnotrevised,eitherreapprovedorwithdrawn.YourcommentsareinvitedeitherforrevisionofthisstandardorforadditionalstandardsandshouldbeaddressedtoASTMInternationalHeadquarters.Yourcommentswillreceivecarefulconsiderationatameetingoftheresponsibletechnicalcommittee,whichyoumayattend.IfyoufeelthatyourcommentshavenotreceivedafairhearingyoushouldmakeyourviewsknowntotheASTMCommitteeonStandards,attheaddressshownbelow.ThisstandardiscopyrightedbyASTMInternational,100BarrHarborDrive,POBoxC700,WestConshohocken,PA19428-2959,UnitedStates.Individualreprints(singleormultiplecopies)ofthisstandardmaybeobtainedbycontactingASTMattheaboveaddressorat610-832-9585(phone),610-832-9555(fax),orservice@astm.org(e-mail);orthroughtheASTMwebsite(www.astm.org).PermissionrightstophotocopythestandardmayalsobesecuredfromtheASTMwebsite(www.astm.org/COPYRIGHT/).A90/A90M−135CopyrightbyASTMInt'l(allrightsreserved);FriAug2303:21:46EDT2013Downloaded/printedbyShanghaiJiaotongUniversitypursuanttoLicenseAgreement.Nofurtherreproductionsauthorized.