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设0<p≤1,级数______。
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对级数则
当p>1时,级数
条件收敛
当p>1时,级数
绝对收敛
当0<p≤1时,级数
绝对收敛
当0<p≤1时,级数
发散
设数列{an}满足条件a0=3a1=1an-2-nn-1an=0n≥2Sx是幂级数的和函数 Ⅰ证明
设Fx是周期为2π的周期函数它在[-ππ]上的表达式为若将Fx展开成傅里叶级数则该级数在x=-3π
-1/2
-π/2
π/2
设a0=4a1=1an-2=nn-1ann≥2.求幂级数[*]的和函数Sx
周期为2π的函数fx它在一个周期上的表达式为设它的傅立叶级数的和函数为Sx则S7π/2的值是
1
-1
0
1/2
设幂级数则该幂级数的收敛半径等于______.
设幂级数的收敛半径为2则幂级数的收敛区间是
(-2,2)
(-2,4)
(0,4)
(-4,0)
设级数的和函数为Sx求 1Sx所满足的一阶微分方程 2Sx的表达式
下列命题正确的是
设级数
与级数
都收敛,则
收敛
设级数
收敛,则级数
与级数
都收敛
若正项级数
发散,则
若正项级数
发散,且un≥vn,则级数
收敛
设fx是周期为2π的周期函数它在[-ππ上的表达式为若将fx展开成傅里叶级数则该级数在x=--π处
-1/2
-π
π/2
设级数a>0当______时级数收敛当______时级数发散.
设fx=1+x0≤x≤1.将fx展开成正弦级数.
设级数收敛则必收敛的级数为
A
B
C
D
设fx在-∞+∞上连续且设an=f0求级数[*]的和
对级数则
当p>1时,级数
条件收敛
当p>1时,级数
绝对收敛
当0<p≤1时,级数
绝对收敛
当0<p≤1时,级数
发散
设fx是周期为2π的周期函数它在[-ππ上的表达式为若将fx展开成傅里叶级数则该级数在x=-π处收敛
-1/2
-π
0
π/2
设0<p≤1级数
绝对收敛
条件收敛
发散
敛散性与p有关
设幂级数∑anx+1n在x=3处条件收敛则该幂级数的收敛半径R为
-1
4
2
3
对于数列我们把称为级数设数列的前项和为如果存在那么级数是收敛的.下列级数中是收敛的有填序号①②③
设Fx是周期为2π的周期函数它在[-ππ]上的表达式为若将Fx展开成傅里叶级数则该级数在x=-3π处
-1/2
-π/2
0
π/2
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Themythologyofaculturecanprovidesomevitalinsightsintothebeliefsandvaluesofthatculture.Byusingfantasticandsometimesincrediblestoriestocreateanoraltraditionbywhichtoexplainthewondersofthenaturalworldandteachlessonstoyoungergenerationsasocietyexposesthoseideasandconceptsheldmostimportant.Justasimportantasthefinallessontobegatheredfromthestorieshoweverarethecharactersandtherolestheyplayinconveyingthatmessage.PerhapstheepitomeofmythologyanditsuseasatooltopassonculturalvaluescanbefoundinAesop’sFablestoldandretoldduringtheeraoftheGreekEmpire.Aesopaslavewhowonthefavorofthecourtthroughhisimaginativeanddescriptivetalesalmostexclusivelyusedanimalstofilltherolesinhisshortstories.Humanswhenatallpresentalmostalwaysplayedthepartofbumblingfoolsstrugglingtolearnthelessonbeingpresented.ThischoiceofcharacterizationallowsustoseethattheGreeksplacedwisdomonalevelslightlybeyondhumansimplyingthatdeepwisdomandunderstandingisauniversalqualitysoughtbyratherthansteanningfromhumanbeings.Aesop’sfablesillustratedthecentralthemesofhumilityandself-reliancereflectingtheimportanceofthosetraitsinearlyGreeksociety.Thefollyofhumanswasusedtocontrastagainsttheultimategoalofattainingahigherlevelofunderstandingandawarenessoftruthsaboutnatureandhumanity.Forexampleonenotablefablefeaturesafoxrepeatedlytryingtoreachabunchofgrapesonaveryhighvine.Afterfailingatseveralattemptsthefoxgivesupmakingupitsmindthatthegrapeswereprobablysouranyway.Thefable’slessonthatweoftenplaydownthatwhichwecan’tachievesoastomakeourselvesfeelbetterteachesthereaderorlistenerinanentertainingwayaboutoneoftheweaknessesofthehumanpsyche.ThemythologyofotherculturesandsocietiesrevealtheunderlyingtraitsoftheirrespectiveculturesjustasAesop’sfablesdid.ThestoriesofRomangodsAztecghostsandEuropeanelvesallservedtotrainancientgenerationsthoselessonsconsideredmostimportanttotheircommunityandtodaytheyofferapowerfullookingglassbywhichtoevaluateandconsiderthecontextualenvironmentinwhichthosecultureexisted.ThemainpurposeofParagraph3isto
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46AnydiscussionoftheAmericaneducationalsystemwouldbelessthancompleteifitdidnotmentiontheemphasisthatmanycollegesanduniversitiesplaceuponthenonacademicsocialextracurricularaspectofeducationoftendefinedaspersonalgrowth.Perhapsausefulwayofviewingthenotionofpersonalgrowthwouldbetopicturetheverylargeandgeneraltermeducationasbeingall-embracingincludingassubsetswithinitacademicandnonacademiccomponents.ThismaybeoneofthemostdifficultconceptstoconveytosomeonewhoisnotintimatelyfamiliarwithAmericanhighereducation.Feweducationalsystemsinothercountriesplacethesameemphasisonthisblendofacademicandpersonaleducation.ThemajorityofcollegesanduniversitiesintheUnitedStatesmakesomeattempttointegratepersonalandintellectualgrowthintheundergraduateyears.47IftheultimategoalofundergraduateeducationinAmericaweresimplytoconveyasetbodyofknowledgethetermofstudiescouldundoubtedlybereduced.Yetthetermsofstudiesareextendedinordertogivestudentsachancetogrowanddevelopinotherways.Numerousopportunitiesaremadeavailabletostudentstobecomeinvolvedinsportsstudentgovernmentmusicalanddramaticorganizationsandcountlessotherorganizedandindividualactivitiesdesignedtoenhanceone’spersonalgrowthandprovidesomerecreationandenjoymentoutsideoftheclassroom.48Experiencewithcampusorganizationsandoff-campuscommunityinvolvementcanbehighlyvaluableinpreparinginternationalstudentsforfutureleadershipintheirprofessionalfieldupontheirreturnhome.ThetypicalAmericancollege’ssupportforextracurricularactivityisperhapsuniqueintheworld.ThisspecialeducationaldimensionbeyondtheclassroomandlaboratoryexperiencedoesnotmeanthatextracurricularparticipationisrequiredtogainanAmericandegree.Itremainsanentirelyoptionalactivitybut49itisnotedherebecauseAmericanshavetraditionallyviewedsuccessinone’sroleasacitizenascloselylinkedtoawell-roundedlifethatincorporatesavarietyofsocialathleticandculturalactivitiesintoaperson’sexperience.AgreatmanyAmericancampusesandcommunitieshaveorganizedspecialextracurricularactivitiesforstudentsfromothercountries.50OnmostcampusesonecanfindaninternationalclubwhichincludesAmericanswherestudentscangettoknowandlearnsociallyfromstudentsfromothercountriesaswellasAmericans.InternationalstudentsarealmostalwaysinvitedthroughorganizedhospitalityactivitiesintothehomesofAmericanslivinginoroutsidetheacademiccommunity.
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LongbeforeManlivedontheEarththerewerefishesreptilesbirdsinsectsandsomemammals.Althoughsomeoftheseanimalswereancestorsofkindslivingtodayothersarenowextinctthatistheyhavenodescendantsalivenow.41Veryoccasionallytherocksshowimpressionofskinsothatapartfromcolorwecanbuildupareasonablyaccuratepictureofananimalthatdiedmillionsofyearsago.Thatkindofrockinwhichtheremainsarefoundtellsusmuchaboutthenatureoftheoriginallandoftenoftheplantsthatgrewonitandevenofitsclimate.42Nearlyallofthefossilsthatweknowwerepreservedinrocksformedbywateractionandmostoftheseareofanimalsthatlivedinornearwater.Thusitfollowsthattheremustbemanykindsofmammalsbirdsandinsectsofwhichweknownothing.43Therewerealsocrablikecreatureswhosebodieswerecoveredwithahornysubstance.Thebodysegmentseachhadtwopairsoflegsonepairforwalkingonthesandybottomtheotherforswimming.Theheadwasakindofshieldwithapairofcompoundeyesoftenwiththousandsoflenses.Theywereusuallyaninchortwolongbutsomewere2feet.44Ofthesetheammonitesareveryinterestingandimportant.Theyhaveashellcomposedofmanychamberseachrepresentingatemporaryhomeoftheanimal.Astheyounggrewlargeritgrewanewchamberandsealedoffthepreviousone.ThousandsofthesecanbeseenintherocksontheDorsetCoast.45About75millionyearsagotheAgeofReptileswasoverandmostofthegroupsdiedout.Themammalsquicklydevelopedandwecantracetheevolutionofmanyfamiliaranimalssuchastheelephantandhorse.Manyofthelatermammalsthoughnowextinctwereknowntoprimitivemanandwerefeaturedbyhimincavepaintingsandonbonecarvings.A.Theshellfishhavealonghistoryintherockandmanydifferentkindsareknown.B.Neverthelessweknowagreatdealaboutmanyofthembecausetheirbonesandshellshavebeenpreservedintherocksasfossilsfromthemwecantelltheirsizeandshapehowtheywalkedthekindoffoodtheyate.C.Thefirstanimalswithtruebackboneswerethefishesfirstknownintherocksof375millionyearsago.About300millionyearsagotheamphibianstheanimalsabletolivebothonlandandinwaterappeared.Theyweregiantsometimes8feetlongandmanyofthemlivedintheswampypoolsinwhichourcoalseamorlayerisformed.Theamphibiansgaverisetothereptilesandfornearly150millionyearstheseweretheprincipalformsoflifeonlandintheseaandintheair.D.Thebestindexfossilstendtobemarinecreatures.Theseanimalsevolvedrapidlyandspreadoverlargeoverlargeareasoftheworld.E.Theearliestanimalswhoseremainshavebeenfoundwereallverysimplekindsandlivedinthesea.Laterformsaremorecomplexandamongthesearethesea-liliesrelationsofthestar-fisheswhichhadlongarmsandwereattachedbyalongstalktotheseabedortorocks.F.Whenananimaldiesthebodyitsbonesorshellmayoftenbecarriedawaybystreamsintolakesortheseaandthengetcoveredupbymud.Iftheanimallivedintheseaitsbodywouldprobablysinkandbecoveredwithmud.Moreandmoremudwouldfalluponituntilthebonesorshellbecomeembeddedandpreserved.G.Manyfactorscaninfluencehowfossilsarepreservedinrocks.Remainsofanorganismmaybereplacedbymineralsdissolvedbyanacidicsolutiontoleaveonlytheirimpressionorsimplyreducedtoamorestableform.
Upuntilafewdecadesagoourvisionsofthefuturewerelargely—thoughbynomeansuniformly—glowinglypositive.Scienceandtechnologywouldcurealltheillsofhumanityleadingtolivesoffulfillmentandopportunityforall.Nowutopiahasgrownunfashionableaswehavegainedadeeperappreciationoftherangeofthreatsfacingusfromasteroidstriketoepidemicflutoclimatechange.Youmightevenbetemptedtoassumethathumanityhaslittlefuturetolookforwardto.Butsuchgloominessismisplaced.Thefossilrecordshowsthatmanyspecieshaveenduredformillionsofyears—sowhyshouldn’tweTakeabroaderlookatourspecies’placeintheuniverseanditbecomesclearthatwehaveanexcellentchanceofsurvivingfortensifnothundredsofthousandsofyears.LookupHomosapiensintheRedListofthreatenedspeciesoftheInternationalUnionfortheConversationofNatureIUCNandyouwillread:ListedasLeastConcernasthespeciesisverywidelydistributedadaptablecurrentlyincreasingandtherearenomajorthreatsresultinginanoverallpopulationdecline.SowhatdoesourdeepfutureholdAgrowingnumberofresearchersandorganizationsarenowthinkingseriouslyaboutthatquestion.ForexampletheLongNowFoundationhasitsflagshipprojectamechanicalclockthatisdesignedtostillbemarkingtimethousandsofyearshence.Perhapswillfullyitmaybeeasiertothinkaboutsuchlengthytimescalesthanaboutthemoreimmediatefuture.Thepotentialevolutionoftoday’stechnologyanditssocialconsequencesisdazzlinglycomplicatedandit’sperhapsbestlefttosciencefictionwritersandfuturologiststoexplorethemanypossibilitieswecanenvisage.That’sonereasonwhywehavelaunchedArcanewpublicationdedicatedtothenearfuture.Buttakealongerviewandthereisasurprisingamountthatwecansaywithconsiderableassurance.Assooftenthepastholdsthekeytothefuture:wehavenowidentifiedenoughofthelong-termpatternsshapingthehistoryoftheplanetandourspeciestomakeevidence-basedforecastsaboutthesituationsinwhichourdescendantswillfindthemselves.Thislongperspectivemakesthepessimisticviewofourprospectsseemmorelikelytobeapassingfad.Tobesurethefutureisnotallrosy.Butwearenowknowledgeableenoughtoreducemanyoftherisksthatthreatenedtheexistenceofearlierhumansandtoimprovethelotofthosetocome.WhichofthefollowingistrueaccordingtoParagraph5
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Sustainabledevelopmentisappliedtojustabouteverythingfromenergytocleanwaterandeconomicgrowthandasaresultithasbecomedifficulttoquestioneitherthebasicassumptionsbehinditorthewaytheconceptisputtouse.Thisisespeciallytrueinagriculturewheresustainabledevelopmentisoftentakenasthesolemeasureofprogresswithoutaproperappreciationofhistoricalandculturalperspectives.Tostartwithitisimportanttorememberthatthenatureofagriculturehaschangedmarkedlythroughouthistoryandwillcontinuetodoso.MedievalagricultureinnorthernEuropefedclothedandshelteredapredominantlyruralsocietywithamuchlowerpopulationdensitythanitistoday.Ithadminimaleffectonbiodiversityandanypollutionitcausedwastypicallylocalized.Intermsofenergyuseandthenutrientscapturedintheproductitwasrelativelyinefficient.Contrastthiswithfarmingsincethestartoftheindustrialrevolution.Competitionfromoverseasledfarmerstospecializeandincreaseyields.Throughoutthisperiodfoodbecamecheapersafeandmorereliable.Howeverthesechangeshavealsoledtohabitatlossandtodiminishingbiodiversity.What’smoredemandforanimalproductsindevelopingcountriesisgrowingsofastthatmeetingitwillrequireanextra300milliontonsofgrainayearby2050.Yetthegrowthofcitiesandindustryisreducingtheamountofwateravailableforagricultureinmanyregions.Allthismeansthatagricultureinthe21stcenturywillhavetobeverydifferentfromhowitwasinthe20th.Thiswillrequireradicalthinking.Forexampleweneedtomoveawayfromtheideathattraditionalpracticesareinevitablymoresustainablethannewones.Wealsoneedtoabandonthenotionthatagriculturecanbezeroimpact.Thekeywillbetoabandontherathersimpleandstaticmeasuresofsustainabilitywhichcentreontheneedtomaintainproductionwithoutincreasingdamage.Insteadweneedamoredynamicinterpretationonethatlooksattheprosandconsofallthevariouswaylandisused.Therearemanydifferentwaystomeasureagriculturalperformancebesidesfoodyield:energyuseenvironmentalcostswaterpuritycarbonfootprintandbiodiversity.ItisclearforexamplethatthecarbonoftransportingtomatoesfromSpaintotheUKislessthanthatofproducingthemintheUKwithadditionalheatingandlighting.Butwedonotknowwhetherlowercarbonfootprintswillalwaysbebetterforbiodiversity.Whatiscrucialisrecognizingthatsustainableagricultureisnotjustaboutsustainablefoodproduction.Whatwillagriculturebelikeinthe21stcentury
Chronicinsomniaisamajorpublichealthproblem.Andtoomanypeopleareusing1therapiesevenwhilethereareafewtreatmentsthatdowork.MillionsofAmericans2awakeatnightcountingsheeporhaveastiffdrinkor3anpillhopingitwillmakethemsleepy.4expertsagreeallthatself-medicatingisabadideaandthecausesofchronicinsomniaremain5.a Chronicinsomniaisamajorpublichealthproblem.Andtoomanypeopleareusing1therapiesevenwhilethereareafewtreatmentsthatdowork.MillionsofAmericans2awakeatnightcountingsheeporhaveastiffdrinkor3anpillhopingitwillmakethemsleepy.4expertsagreeallthatself-medicatingisabadideaandthecausesofchronicinsomniaremain5. Almostathirdofadultshavetroublesleepingandabout10percenthave6ofdaytimeimpairmentthatsignaltrueinsomnia.But7thecomplaintsscientistsknowsurprisinglylittleaboutwhatcauseschronicinsomniaitshealthconsequencesandhowbesttotreatitapanelofspecialists8togetherbytheNationalInstitutesofHealthconcludedWednesday.Thepanelcalled9abroadrangeofresearchintoinsomnia10thatifscientistsunderstoodits11causestheycoulddevelopbettertreatments. Mostbutnotallinsomniaisthoughtto12otherhealthproblemsfromarthritisanddepressiontocardiovasculardisease.Thequestionofteniswhethertheinsomniacamefirstorwasaresultoftheotherdiseasesandhowtroublesleepingin13complicatesthoseotherproblems.Otherdiseases14theriskofinsomniaseemstoincreasewithageandtobemore15amongwomenespeciallyaftertheir50s.Smokingcaffeineandnumerous16drugsalsoaffectsleep. TheNIHisspendingabout$200millionthisyearonsleep-relatedresearchsome17tospecificdisordersandothers18theunderlyingscientificlawsthatcontrolthenervoussystemofsleep.Theagencywas19thepane’sreviewbeforedecidingwhatadditionalworkshouldbe20atinsomnia. 19
设A=ijn×n是正交矩阵将A以行分块为A=α1α2αnT则方程组AX=bb=b1bnT的通解为______
Upuntilafewdecadesagoourvisionsofthefuturewerelargely—thoughbynomeansuniformly—glowinglypositive.Scienceandtechnologywouldcurealltheillsofhumanityleadingtolivesoffulfillmentandopportunityforall.Nowutopiahasgrownunfashionableaswehavegainedadeeperappreciationoftherangeofthreatsfacingusfromasteroidstriketoepidemicflutoclimatechange.Youmightevenbetemptedtoassumethathumanityhaslittlefuturetolookforwardto.Butsuchgloominessismisplaced.Thefossilrecordshowsthatmanyspecieshaveenduredformillionsofyears—sowhyshouldn’tweTakeabroaderlookatourspecies’placeintheuniverseanditbecomesclearthatwehaveanexcellentchanceofsurvivingfortensifnothundredsofthousandsofyears.LookupHomosapiensintheRedListofthreatenedspeciesoftheInternationalUnionfortheConversationofNatureIUCNandyouwillread:ListedasLeastConcernasthespeciesisverywidelydistributedadaptablecurrentlyincreasingandtherearenomajorthreatsresultinginanoverallpopulationdecline.SowhatdoesourdeepfutureholdAgrowingnumberofresearchersandorganizationsarenowthinkingseriouslyaboutthatquestion.ForexampletheLongNowFoundationhasitsflagshipprojectamechanicalclockthatisdesignedtostillbemarkingtimethousandsofyearshence.Perhapswillfullyitmaybeeasiertothinkaboutsuchlengthytimescalesthanaboutthemoreimmediatefuture.Thepotentialevolutionoftoday’stechnologyanditssocialconsequencesisdazzlinglycomplicatedandit’sperhapsbestlefttosciencefictionwritersandfuturologiststoexplorethemanypossibilitieswecanenvisage.That’sonereasonwhywehavelaunchedArcanewpublicationdedicatedtothenearfuture.Buttakealongerviewandthereisasurprisingamountthatwecansaywithconsiderableassurance.Assooftenthepastholdsthekeytothefuture:wehavenowidentifiedenoughofthelong-termpatternsshapingthehistoryoftheplanetandourspeciestomakeevidence-basedforecastsaboutthesituationsinwhichourdescendantswillfindthemselves.Thislongperspectivemakesthepessimisticviewofourprospectsseemmorelikelytobeapassingfad.Tobesurethefutureisnotallrosy.Butwearenowknowledgeableenoughtoreducemanyoftherisksthatthreatenedtheexistenceofearlierhumansandtoimprovethelotofthosetocome.Whichofthefollowingwouldbethebesttitleforthetext
Chronicinsomniaisamajorpublichealthproblem.Andtoomanypeopleareusing1therapiesevenwhilethereareafewtreatmentsthatdowork.MillionsofAmericans2awakeatnightcountingsheeporhaveastiffdrinkor3anpillhopingitwillmakethemsleepy.4expertsagreeallthatself-medicatingisabadideaandthecausesofchronicinsomniaremain5.a Chronicinsomniaisamajorpublichealthproblem.Andtoomanypeopleareusing1therapiesevenwhilethereareafewtreatmentsthatdowork.MillionsofAmericans2awakeatnightcountingsheeporhaveastiffdrinkor3anpillhopingitwillmakethemsleepy.4expertsagreeallthatself-medicatingisabadideaandthecausesofchronicinsomniaremain5. Almostathirdofadultshavetroublesleepingandabout10percenthave6ofdaytimeimpairmentthatsignaltrueinsomnia.But7thecomplaintsscientistsknowsurprisinglylittleaboutwhatcauseschronicinsomniaitshealthconsequencesandhowbesttotreatitapanelofspecialists8togetherbytheNationalInstitutesofHealthconcludedWednesday.Thepanelcalled9abroadrangeofresearchintoinsomnia10thatifscientistsunderstoodits11causestheycoulddevelopbettertreatments. Mostbutnotallinsomniaisthoughtto12otherhealthproblemsfromarthritisanddepressiontocardiovasculardisease.Thequestionofteniswhethertheinsomniacamefirstorwasaresultoftheotherdiseasesandhowtroublesleepingin13complicatesthoseotherproblems.Otherdiseases14theriskofinsomniaseemstoincreasewithageandtobemore15amongwomenespeciallyaftertheir50s.Smokingcaffeineandnumerous16drugsalsoaffectsleep. TheNIHisspendingabout$200millionthisyearonsleep-relatedresearchsome17tospecificdisordersandothers18theunderlyingscientificlawsthatcontrolthenervoussystemofsleep.Theagencywas19thepane’sreviewbeforedecidingwhatadditionalworkshouldbe20atinsomnia. 15
Themythologyofaculturecanprovidesomevitalinsightsintothebeliefsandvaluesofthatculture.Byusingfantasticandsometimesincrediblestoriestocreateanoraltraditionbywhichtoexplainthewondersofthenaturalworldandteachlessonstoyoungergenerationsasocietyexposesthoseideasandconceptsheldmostimportant.Justasimportantasthefinallessontobegatheredfromthestorieshoweverarethecharactersandtherolestheyplayinconveyingthatmessage.PerhapstheepitomeofmythologyanditsuseasatooltopassonculturalvaluescanbefoundinAesop’sFablestoldandretoldduringtheeraoftheGreekEmpire.Aesopaslavewhowonthefavorofthecourtthroughhisimaginativeanddescriptivetalesalmostexclusivelyusedanimalstofilltherolesinhisshortstories.Humanswhenatallpresentalmostalwaysplayedthepartofbumblingfoolsstrugglingtolearnthelessonbeingpresented.ThischoiceofcharacterizationallowsustoseethattheGreeksplacedwisdomonalevelslightlybeyondhumansimplyingthatdeepwisdomandunderstandingisauniversalqualitysoughtbyratherthansteanningfromhumanbeings.Aesop’sfablesillustratedthecentralthemesofhumilityandself-reliancereflectingtheimportanceofthosetraitsinearlyGreeksociety.Thefollyofhumanswasusedtocontrastagainsttheultimategoalofattainingahigherlevelofunderstandingandawarenessoftruthsaboutnatureandhumanity.Forexampleonenotablefablefeaturesafoxrepeatedlytryingtoreachabunchofgrapesonaveryhighvine.Afterfailingatseveralattemptsthefoxgivesupmakingupitsmindthatthegrapeswereprobablysouranyway.Thefable’slessonthatweoftenplaydownthatwhichwecan’tachievesoastomakeourselvesfeelbetterteachesthereaderorlistenerinanentertainingwayaboutoneoftheweaknessesofthehumanpsyche.ThemythologyofotherculturesandsocietiesrevealtheunderlyingtraitsoftheirrespectiveculturesjustasAesop’sfablesdid.ThestoriesofRomangodsAztecghostsandEuropeanelvesallservedtotrainancientgenerationsthoselessonsconsideredmostimportanttotheircommunityandtodaytheyofferapowerfullookingglassbywhichtoevaluateandconsiderthecontextualenvironmentinwhichthosecultureexisted.Themainpointofthistextis
Donotsignyourownnameattheendoftheletter.Use"DepartmentofChineseLanguageandLiterature"instead. Donotwritetheaddress.
Themythologyofaculturecanprovidesomevitalinsightsintothebeliefsandvaluesofthatculture.Byusingfantasticandsometimesincrediblestoriestocreateanoraltraditionbywhichtoexplainthewondersofthenaturalworldandteachlessonstoyoungergenerationsasocietyexposesthoseideasandconceptsheldmostimportant.Justasimportantasthefinallessontobegatheredfromthestorieshoweverarethecharactersandtherolestheyplayinconveyingthatmessage.PerhapstheepitomeofmythologyanditsuseasatooltopassonculturalvaluescanbefoundinAesop’sFablestoldandretoldduringtheeraoftheGreekEmpire.Aesopaslavewhowonthefavorofthecourtthroughhisimaginativeanddescriptivetalesalmostexclusivelyusedanimalstofilltherolesinhisshortstories.Humanswhenatallpresentalmostalwaysplayedthepartofbumblingfoolsstrugglingtolearnthelessonbeingpresented.ThischoiceofcharacterizationallowsustoseethattheGreeksplacedwisdomonalevelslightlybeyondhumansimplyingthatdeepwisdomandunderstandingisauniversalqualitysoughtbyratherthansteanningfromhumanbeings.Aesop’sfablesillustratedthecentralthemesofhumilityandself-reliancereflectingtheimportanceofthosetraitsinearlyGreeksociety.Thefollyofhumanswasusedtocontrastagainsttheultimategoalofattainingahigherlevelofunderstandingandawarenessoftruthsaboutnatureandhumanity.Forexampleonenotablefablefeaturesafoxrepeatedlytryingtoreachabunchofgrapesonaveryhighvine.Afterfailingatseveralattemptsthefoxgivesupmakingupitsmindthatthegrapeswereprobablysouranyway.Thefable’slessonthatweoftenplaydownthatwhichwecan’tachievesoastomakeourselvesfeelbetterteachesthereaderorlistenerinanentertainingwayaboutoneoftheweaknessesofthehumanpsyche.ThemythologyofotherculturesandsocietiesrevealtheunderlyingtraitsoftheirrespectiveculturesjustasAesop’sfablesdid.ThestoriesofRomangodsAztecghostsandEuropeanelvesallservedtotrainancientgenerationsthoselessonsconsideredmostimportanttotheircommunityandtodaytheyofferapowerfullookingglassbywhichtoevaluateandconsiderthecontextualenvironmentinwhichthosecultureexisted.Theauthorappearstoviewfablesas
A是n阶矩阵且A3=0则______
设X服从正态分布N022而X1X2X15为来自总体X的简单随机样本则随机变量所服从的分布为______
Inapurelybiologicalsensefearbeginswiththebody’ssystemforreactingtothingsthatcanharmus—theso-calledfight-or-flightresponse."Ananimalthatcan’tdetectdangercan’tstayalive"saysJosephLeDoux.Likeanimalshumansevolvedwithanelaboratemechanismforprocessinginformationaboutpotentialthreats.Atitscoreisaclusterofneuronsdeepinthebrainknownastheamygdala. LeDouxstudiesthewayanimalsandhumansrespondtothreatstounderstandhowweformmemoriesofsignificanteventsinourlives.Theamygdalareceivesinputfrommanypartsofthebrainincludingregionsresponsibleforretrievingmemories.Usingthisinformationtheamygdalaappraisesasituation—Ithinkthischargingdogwantstobiteme—andtriggersaresponsebyradiatingnervesignalsthroughoutthebody.Thesesignalsproducethefamiliarsignsofdistress:tremblingperspirationandfast-movingfeetjusttonamethree. Thisfearmechanismiscriticaltothesurvivalofallanimalsbutnoonecansayforsurewhetherbeastsotherthanhumansknowthey’reafraid.ThatisasLeDouxsays"ifyouputthatsystemintoabrainthathasconsciousnessthenyougetthefeelingoffear." HumanssaysEdwardM.Hallowellhavetheabilitytocallupimagesofbadthingsthathappenedinthepastandtoanticipatefutureevents.Combinethesehigherthoughtprocesseswithourhardwireddangerdetectionsystemsandyougetanear-universalhumanphenomenon:worry. That’snotnecessarilyabadthingsaysHallowell."Whenusedproperlyworryisanincredibledevice"hesays.Afterallalittlehealthyworryingisokayifitleadstoconstructiveaction—likehavingadoctorlookatthatweirdspotonyourback. Hallowellinsiststhoughthatthere’sarightwaytoworry."Neverdoitalonegetthefactsandthenmakeaplan."Hesays.Mostofushavesurvivedarecessionsowe’refamiliarwiththebelt-tighteningstrategiesneededtosurviveaslump. Unfortunatelyfewofushavemuchexperiencedealingwiththethreatofterrorismsoit’sbeendifficulttogetfactabouthowweshouldrespond.That’swhyHallowellbelievesitwasokayforpeopletoindulgesomeextremeworrieslastfallbyaskingdoctorsforCiproandbuyinggasmasks. WhichofthefollowingisthebestwaytodealWithyourworriesaccordingtoHallowell
=______
Chronicinsomniaisamajorpublichealthproblem.Andtoomanypeopleareusing1therapiesevenwhilethereareafewtreatmentsthatdowork.MillionsofAmericans2awakeatnightcountingsheeporhaveastiffdrinkor3anpillhopingitwillmakethemsleepy.4expertsagreeallthatself-medicatingisabadideaandthecausesofchronicinsomniaremain5.a Chronicinsomniaisamajorpublichealthproblem.Andtoomanypeopleareusing1therapiesevenwhilethereareafewtreatmentsthatdowork.MillionsofAmericans2awakeatnightcountingsheeporhaveastiffdrinkor3anpillhopingitwillmakethemsleepy.4expertsagreeallthatself-medicatingisabadideaandthecausesofchronicinsomniaremain5. Almostathirdofadultshavetroublesleepingandabout10percenthave6ofdaytimeimpairmentthatsignaltrueinsomnia.But7thecomplaintsscientistsknowsurprisinglylittleaboutwhatcauseschronicinsomniaitshealthconsequencesandhowbesttotreatitapanelofspecialists8togetherbytheNationalInstitutesofHealthconcludedWednesday.Thepanelcalled9abroadrangeofresearchintoinsomnia10thatifscientistsunderstoodits11causestheycoulddevelopbettertreatments. Mostbutnotallinsomniaisthoughtto12otherhealthproblemsfromarthritisanddepressiontocardiovasculardisease.Thequestionofteniswhethertheinsomniacamefirstorwasaresultoftheotherdiseasesandhowtroublesleepingin13complicatesthoseotherproblems.Otherdiseases14theriskofinsomniaseemstoincreasewithageandtobemore15amongwomenespeciallyaftertheir50s.Smokingcaffeineandnumerous16drugsalsoaffectsleep. TheNIHisspendingabout$200millionthisyearonsleep-relatedresearchsome17tospecificdisordersandothers18theunderlyingscientificlawsthatcontrolthenervoussystemofsleep.Theagencywas19thepane’sreviewbeforedecidingwhatadditionalworkshouldbe20atinsomnia. 11
Inapurelybiologicalsensefearbeginswiththebody’ssystemforreactingtothingsthatcanharmus—theso-calledfight-or-flightresponse.Ananimalthatcan’tdetectdangercan’tstayalivesaysJosephLeDoux.Likeanimalshumansevolvedwithanelaboratemechanismforprocessinginformationaboutpotentialthreats.Atitscoreisaclusterofneuronsdeepinthebrainknownastheamygdala.LeDouxstudiesthewayanimalsandhumansrespondtothreatstounderstandhowweformmemoriesofsignificanteventsinourlives.Theamygdalareceivesinputfrommanypartsofthebrainincludingregionsresponsibleforretrievingmemories.Usingthisinformationtheamygdalaappraisesasituation—Ithinkthischargingdogwantstobiteme—andtriggersaresponsebyradiatingnervesignalsthroughoutthebody.Thesesignalsproducethefamiliarsignsofdistress:tremblingperspirationandfast-movingfeetjusttonamethree.Thisfearmechanismiscriticaltothesurvivalofallanimalsbutnoonecansayforsurewhetherbeastsotherthanhumansknowthey’reafraid.ThatisasLeDouxsaysifyouputthatsystemintoabrainthathasconsciousnessthenyougetthefeelingoffear.HumanssaysEdwardM.Hallowellhavetheabilitytocallupimagesofbadthingsthathappenedinthepastandtoanticipatefutureevents.Combinethesehigherthoughtprocesseswithourhardwireddangerdetectionsystemsandyougetanear-universalhumanphenomenon:worry.That’snotnecessarilyabadthingsaysHallowell.Whenusedproperlyworryisanincredibledevicehesays.Afterallalittlehealthyworryingisokayifitleadstoconstructiveaction—likehavingadoctorlookatthatweirdspotonyourback.Hallowellinsiststhoughthatthere’sarightwaytoworry.Neverdoitalonegetthefactsandthenmakeaplan.Hesays.Mostofushavesurvivedarecessionsowe’refamiliarwiththebelt-tighteningstrategiesneededtosurviveaslump.Unfortunatelyfewofushavemuchexperiencedealingwiththethreatofterrorismsoit’sbeendifficulttogetfactabouthowweshouldrespond.That’swhyHallowellbelievesitwasokayforpeopletoindulgesomeextremeworrieslastfallbyaskingdoctorsforCiproandbuyinggasmasks.FromthestudiesconductedbyLeDouxwelearnthat
Upuntilafewdecadesagoourvisionsofthefuturewerelargely—thoughbynomeansuniformly—glowinglypositive.Scienceandtechnologywouldcurealltheillsofhumanityleadingtolivesoffulfillmentandopportunityforall.Nowutopiahasgrownunfashionableaswehavegainedadeeperappreciationoftherangeofthreatsfacingusfromasteroidstriketoepidemicflutoclimatechange.Youmightevenbetemptedtoassumethathumanityhaslittlefuturetolookforwardto.Butsuchgloominessismisplaced.Thefossilrecordshowsthatmanyspecieshaveenduredformillionsofyears—sowhyshouldn’tweTakeabroaderlookatourspecies’placeintheuniverseanditbecomesclearthatwehaveanexcellentchanceofsurvivingfortensifnothundredsofthousandsofyears.LookupHomosapiensintheRedListofthreatenedspeciesoftheInternationalUnionfortheConversationofNatureIUCNandyouwillread:ListedasLeastConcernasthespeciesisverywidelydistributedadaptablecurrentlyincreasingandtherearenomajorthreatsresultinginanoverallpopulationdecline.SowhatdoesourdeepfutureholdAgrowingnumberofresearchersandorganizationsarenowthinkingseriouslyaboutthatquestion.ForexampletheLongNowFoundationhasitsflagshipprojectamechanicalclockthatisdesignedtostillbemarkingtimethousandsofyearshence.Perhapswillfullyitmaybeeasiertothinkaboutsuchlengthytimescalesthanaboutthemoreimmediatefuture.Thepotentialevolutionoftoday’stechnologyanditssocialconsequencesisdazzlinglycomplicatedandit’sperhapsbestlefttosciencefictionwritersandfuturologiststoexplorethemanypossibilitieswecanenvisage.That’sonereasonwhywehavelaunchedArcanewpublicationdedicatedtothenearfuture.Buttakealongerviewandthereisasurprisingamountthatwecansaywithconsiderableassurance.Assooftenthepastholdsthekeytothefuture:wehavenowidentifiedenoughofthelong-termpatternsshapingthehistoryoftheplanetandourspeciestomakeevidence-basedforecastsaboutthesituationsinwhichourdescendantswillfindthemselves.Thislongperspectivemakesthepessimisticviewofourprospectsseemmorelikelytobeapassingfad.Tobesurethefutureisnotallrosy.Butwearenowknowledgeableenoughtoreducemanyoftherisksthatthreatenedtheexistenceofearlierhumansandtoimprovethelotofthosetocome.Ourvisionofthefutureusedtobeinspiredby
LongbeforeManlivedontheEarththerewerefishesreptilesbirdsinsectsandsomemammals.Althoughsomeoftheseanimalswereancestorsofkindslivingtodayothersarenowextinctthatistheyhavenodescendantsalivenow.41Veryoccasionallytherocksshowimpressionofskinsothatapartfromcolorwecanbuildupareasonablyaccuratepictureofananimalthatdiedmillionsofyearsago.Thatkindofrockinwhichtheremainsarefoundtellsusmuchaboutthenatureoftheoriginallandoftenoftheplantsthatgrewonitandevenofitsclimate.42Nearlyallofthefossilsthatweknowwerepreservedinrocksformedbywateractionandmostoftheseareofanimalsthatlivedinornearwater.Thusitfollowsthattheremustbemanykindsofmammalsbirdsandinsectsofwhichweknownothing.43Therewerealsocrablikecreatureswhosebodieswerecoveredwithahornysubstance.Thebodysegmentseachhadtwopairsoflegsonepairforwalkingonthesandybottomtheotherforswimming.Theheadwasakindofshieldwithapairofcompoundeyesoftenwiththousandsoflenses.Theywereusuallyaninchortwolongbutsomewere2feet.44Ofthesetheammonitesareveryinterestingandimportant.Theyhaveashellcomposedofmanychamberseachrepresentingatemporaryhomeoftheanimal.Astheyounggrewlargeritgrewanewchamberandsealedoffthepreviousone.ThousandsofthesecanbeseenintherocksontheDorsetCoast.45About75millionyearsagotheAgeofReptileswasoverandmostofthegroupsdiedout.Themammalsquicklydevelopedandwecantracetheevolutionofmanyfamiliaranimalssuchastheelephantandhorse.Manyofthelatermammalsthoughnowextinctwereknowntoprimitivemanandwerefeaturedbyhimincavepaintingsandonbonecarvings.A.Theshellfishhavealonghistoryintherockandmanydifferentkindsareknown.B.Neverthelessweknowagreatdealaboutmanyofthembecausetheirbonesandshellshavebeenpreservedintherocksasfossilsfromthemwecantelltheirsizeandshapehowtheywalkedthekindoffoodtheyate.C.Thefirstanimalswithtruebackboneswerethefishesfirstknownintherocksof375millionyearsago.About300millionyearsagotheamphibianstheanimalsabletolivebothonlandandinwaterappeared.Theyweregiantsometimes8feetlongandmanyofthemlivedintheswampypoolsinwhichourcoalseamorlayerisformed.Theamphibiansgaverisetothereptilesandfornearly150millionyearstheseweretheprincipalformsoflifeonlandintheseaandintheair.D.Thebestindexfossilstendtobemarinecreatures.Theseanimalsevolvedrapidlyandspreadoverlargeoverlargeareasoftheworld.E.Theearliestanimalswhoseremainshavebeenfoundwereallverysimplekindsandlivedinthesea.Laterformsaremorecomplexandamongthesearethesea-liliesrelationsofthestar-fisheswhichhadlongarmsandwereattachedbyalongstalktotheseabedortorocks.F.Whenananimaldiesthebodyitsbonesorshellmayoftenbecarriedawaybystreamsintolakesortheseaandthengetcoveredupbymud.Iftheanimallivedintheseaitsbodywouldprobablysinkandbecoveredwithmud.Moreandmoremudwouldfalluponituntilthebonesorshellbecomeembeddedandpreserved.G.Manyfactorscaninfluencehowfossilsarepreservedinrocks.Remainsofanorganismmaybereplacedbymineralsdissolvedbyanacidicsolutiontoleaveonlytheirimpressionorsimplyreducedtoamorestableform.
若=+∞则级数______
设ab为正常系数λ为非负常数微分方程Ⅰ求该方程的通解Ⅱ证明当λ=0时当λ>0时
设z=f2x-yysinx其中fuv具有连续的二阶偏导数求
______.
46AnydiscussionoftheAmericaneducationalsystemwouldbelessthancompleteifitdidnotmentiontheemphasisthatmanycollegesanduniversitiesplaceuponthenonacademicsocialextracurricularaspectofeducationoftendefinedaspersonalgrowth.Perhapsausefulwayofviewingthenotionofpersonalgrowthwouldbetopicturetheverylargeandgeneraltermeducationasbeingall-embracingincludingassubsetswithinitacademicandnonacademiccomponents.ThismaybeoneofthemostdifficultconceptstoconveytosomeonewhoisnotintimatelyfamiliarwithAmericanhighereducation.Feweducationalsystemsinothercountriesplacethesameemphasisonthisblendofacademicandpersonaleducation.ThemajorityofcollegesanduniversitiesintheUnitedStatesmakesomeattempttointegratepersonalandintellectualgrowthintheundergraduateyears.47IftheultimategoalofundergraduateeducationinAmericaweresimplytoconveyasetbodyofknowledgethetermofstudiescouldundoubtedlybereduced.Yetthetermsofstudiesareextendedinordertogivestudentsachancetogrowanddevelopinotherways.Numerousopportunitiesaremadeavailabletostudentstobecomeinvolvedinsportsstudentgovernmentmusicalanddramaticorganizationsandcountlessotherorganizedandindividualactivitiesdesignedtoenhanceone’spersonalgrowthandprovidesomerecreationandenjoymentoutsideoftheclassroom.48Experiencewithcampusorganizationsandoff-campuscommunityinvolvementcanbehighlyvaluableinpreparinginternationalstudentsforfutureleadershipintheirprofessionalfieldupontheirreturnhome.ThetypicalAmericancollege’ssupportforextracurricularactivityisperhapsuniqueintheworld.ThisspecialeducationaldimensionbeyondtheclassroomandlaboratoryexperiencedoesnotmeanthatextracurricularparticipationisrequiredtogainanAmericandegree.Itremainsanentirelyoptionalactivitybut49itisnotedherebecauseAmericanshavetraditionallyviewedsuccessinone’sroleasacitizenascloselylinkedtoawell-roundedlifethatincorporatesavarietyofsocialathleticandculturalactivitiesintoaperson’sexperience.AgreatmanyAmericancampusesandcommunitieshaveorganizedspecialextracurricularactivitiesforstudentsfromothercountries.50OnmostcampusesonecanfindaninternationalclubwhichincludesAmericanswherestudentscangettoknowandlearnsociallyfromstudentsfromothercountriesaswellasAmericans.InternationalstudentsarealmostalwaysinvitedthroughorganizedhospitalityactivitiesintothehomesofAmericanslivinginoroutsidetheacademiccommunity.
若函数y=fx有f’x0=则当Δx→0时该函数在x=x0点外的微分dy是______
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