Unit1ExercisesTranslatethefollowingsentencesintoChinese.Aswithseriesresonance,thegreatertheresistanceinthecircuitthelowertheQand,accordingly,theflatterandbroadertheresonancecurveofeitherlinecurrentorcircuitimpedance.對于串聯諧振,電路中的電阻愈大Q值就愈低,相應地線路電流或電路阻抗的諧振曲線也就愈平、愈寬.Awirecarryingacurrentlooksexactlythesameandweighsexactlythesameasitdoeswhenitisnotcarryingacurrent.一根帶電的導線其外表與重量都與不帶電導線完全一樣.Clickmouseonthewaveformanddragittochangethepulserepetitionrate,ordirectlyenteranewvalueoftheperiodintheprovideddialoguebox,whilekeepingthepulsewidthunchanged.在波形上點擊鼠標并拖動來改變脈沖重復頻率,或者在提供的對話框中直接輸入新的周期值,而保持脈沖寬度不變.Electronicsisthescienceandthetechnologyofthepassageofchargedparticlesinagas,inavacuum,orinasemiconductor.Pleasenotethatparticlemotionconfinedwithinametalonlyisnotconsideredelectronics.電子學是一門有關帶電粒子在氣體、真空或半導體中運動的科學技術.注意,在本書中粒子運動僅限于金屬的情況不屬于電子學.Hardwaretechnologieshaveplayedvitalrolesinourabilitytouseelectronicpropertiestoprocessinformation,butsoftwareanddataprocessingaspectshavenotdevelopedatthesamespeed.硬件技術在我們使用電子特性來處理信息的水平中一直起著重要作用,而軟件及數字處理方面卻沒能與硬件同步開展.However,inaproperlydesignedDCamplifiertheeffectoftransistorparametervariation,otherthanIco,maybepracticallyeliminatediftheoperationpointofeachstageisadjustedsothatitremainsinthelinearoperationrangeofthetransistorastemperaturevaries.然而在設計得當的直流放大器中,假設調節每一級的工作點使之在溫度變化時保持在晶體管線性區,就能在實際上消除Ico以外的晶體管參數變化所造成的影響.Unit2Exercises⑴TranslatethefollowingsentencesintoChinese.Ifanalogsignalsaretobetransmitteddigitally,theyfirsthavetobesampledataspecifiedrateandfurtherconvertedtodiscreteamplitudesamplesbyquantization.如果要以數字方式傳輸模擬信號,首先必須以一定的頻率對信號進行采樣,然后通過量化進一步將它們轉換為離散的幅度樣本.Linearfiltersamplifyorattenuateselectedspatialfrequencies,canachievesucheffectsassmoothingandsharpening,andusuallyformthebasisofre-samplingandboundarydetectionalgorithms.線性濾波器放大或衰減選擇的空間頻率,能夠實現像平滑和銳化這些效果,通常是重采樣和邊緣檢測算法的根底.Stabilityandrepeatabilityarefundamentalattributesofdigitalcircuits,however,andthenecessaryaccuracycanbeobtainedinadigitalversionofthemodulatorbyanappropriatechoiceofwordlengthtorepresentthesignals.不過穩定性和可重復性是數字電路的根本性質,在數字式調制器中必要的精度可通過適當地選擇代表信號的字長而獲得.Thefirstobservationismadeonthefundamentalrelationshipbetweenthenatureofsystemandtheperiodicityofitsfrequencyresponse:acontinuoussystemhasanaperiodicfrequencyresponse,whileadiscretesystemhasaperiodicfrequencyresponse.從系統性質和它頻率響應的周期性之間的根本關系中首先可以看到：連續系統有非周期性的頻率響應,而離散系統有周期性的頻率響應.Themainfunctionofthereceiveristoextracttheinputmessagesignalfromthedegradedversionofthetransmittedsignalcomingfromthechannel.接收器的主要功能是從由信道傳輸來的退化了的信號中提取出輸入消息.Unit3Exercises⑴TranslatethefollowingsentencesintoChinese.Averycommonlyusedmethodofmicrowavemeasurementsisbasedonthestudyofastandingwavepatternformedalongthelinebecauseoftheinterferenceofincidentandreflectedwaves.一個很常用的微波測量方法是基于對駐波圖型的研究,這種駐波是由入射波和反射波之間的干預而沿著傳輸線形成的.Computationsshowareductionof6dBintheEMfieldintensitywiththedistancedoubled,andanincreaseof3dBintheintensitywiththetransmittedpowerdoubled.Thisresultprovidesverificationtothealgorithmused.計算說明,當距離增大一倍時,電磁場強度減小6分貝；而發射功率增大一倍時,場強那么增加貝.這一結果驗證了所用算法的正確性.Liketransferofheatbyconduction,convectionandradiation,microwaveheatingcanbeconsideredasanothermodeofheattransfer,inwhichheatisproduceddirectlyatthelocationofthedielectriclosses.就像通過傳導、對流、輻射來傳遞熱量一樣,微波加熱可以看作熱傳遞的另一種方式,即熱量直接產生于發生介電損耗的地方.Operationoftheradarisbasedonthemeasurementofthetimeittakesforapulsetransmittedfromanantennatogetreflectedbytheobjecttobedetectedandtoreturnattheantennaandthereceiver.雷達的工作是基于對天線發出的脈沖被所要探測的目標反射,〔然后〕回到天線和接收機所需時間的測量.OthermotivationsforusingCADincircuitdesignincludesthewishtoacquireconfidenceinadesignthatwasaccomplishedbyothermeans,and,notleastinimportance,asenseofcuriosityorperhapsadesiretodiscovertheunexpected.在電路設計中使用CAD的其它動機包括：想要驗證用別的方法設計出來的電路；滿足好奇心或者可能是想發現預想不到的現象.后一個動機并非是最不重要的.〔取得信心,并非最不重要,意料之外的事〕Thespacingbetweentherepeatingamplifiersisafunctionofthecableattenuationandthesystembandwidthsothatthegainprovidedbytheseamplifierscompensatesforthelossintroducedbythecable.中繼放大器之間的間距是電纜衰減和系統帶寬的函數,以便這些放大器提供的增益補償電纜引起的損耗.Whenthecut-offfrequencyisnolessthanthemaximalfrequencyoftheoriginalsignal,norisitgreaterthanthedifferencebetweenthesamplingfrequencyandthemaximalfrequency,theoriginalsignalmaybecompletelyrebuilt.當截止頻率不小于原始信號的最高頻率,也不大于采樣頻率和最高頻率之差,原始信號可以完整地重建.WhilethepoliticsofthelastonehundredyearscenteredaroundIndustrialAgetechnology,thepoliticsofthefuturewillbebasedonInformationAgeconcernsorientedtowardsthestorage,protectionandexchangeofinformation.盡管近百年來的政治活動是以工業時代的技術為中央的,未來的政治活動將基于信息時代的事物,面向信息的存儲、保護和交換.Unit4Exercises⑴TranslatethefollowingpassagesintoChinese.Communicationmaybebroadlydefinedasthetransferofinformationfromonepointtoanother.Whentheinformationistobeconveyedoveranydistanceacommunicationsystemisusuallyrequired.Withinacommunicationsystemtheinformationtransferisfrequentlyachievedbysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrierfortheinformationsignal.Thismodulatedcarrieristhentransmittedtotherequireddestinationwhereitisreceivedandtheoriginalinformationsignalisobtainedbydemodulation.Sophisticatedtechniqueshavebeendevelopedforthisprocessbyusingelectromagneticcarrierwavesoperatingatradiofrequenciesaswellasmicrowaveandmillimeterwavefrequencies.

However,communicationmayalsobeachievedbyusinganelectromagneticcarrierthatisselectedfromtheopticalrangeoffrequencies.通信可以廣義地定義為從一處到另一處的信息傳遞.當要將信息傳輸到任何距離以外時就需要有一個通信系統.在通信系統內部,信息的傳輸經常通過將信息疊加或調制到作為信號載體的電磁波上來實現.經調制的載波然后被傳送到要求的目的地,在那里被接收,原始信號通過解調被恢復出來.為了實現這一過程,已經利用工作在射頻、微波以及毫米波頻率上的電磁載波開發了復雜的技術.不過通信也可以用光波頻段上的電磁載波來實現.Electroniccommunicationsisthetransferandmovementofdatabetweenlocationsthroughtheuseofcomputers.Anelectroniccommunicationsystemincludestheequipmentneededtosupportthemovementofinformation,thecommunicationlinesandmediatocarrytheinformation,thecomputersoftwareandprogramstocontroltheflowofinformation,thepersonneltoplan,implement,andoperatecommunications,andthemanagementofalltheseresources.Electroniccommunicationsestablisheslinksbetweenpeopleaswellascomputers.電子通信就是通過使用計算機在不同的地點之間傳輸數據.一個電子通信系統包括：支持信息流動所需要的設備,承載信息的通信線路和媒介,限制信息流的計算機軟件和程序,方案、實施、操作通信系統的人員,以及對所有這些資源的治理.電子通信建立起人和人、計算機和計算機之間的聯系.Firstgenerationcommunicationssystemscanbecharacterizedbytheuseofanalogtransmissiontechniques,andtheuseofsimplemultiplexaccesstechniquessuchasfrequencydivisionmultipleaccess(FDMA).Theysufferedfromalowusercapacity,andintroducedintheearly1990securityproblemsduetothesimpleradiointerfaceused.Secintroducedintheearly1990's,andallusedigitaltechnology.Thisprovidedanincreaseintheusercapacityofaroundthreetimes,achievedbycompressingthevoicewaveformsbeforetransmission.Thirdgenerationsystemsareanextensiononthecomplexityofsecond-generationsystemsandaretobeintroducedaftertheyear2000.Thesystemcapacitywillbeincreasedtoovertentimesoriginalfirstgenerationsystems,achievedbyusingcomplexmultiplexaccesstechniquessuchascodedivisionmultiplexaccess(CDMA),oranextensionofTDMA,andbyimprovingflexibilityofservicesavailable.第一代通信系統以模擬傳輸技術和簡單復用技術如頻分復用為特征.這些系統用戶容量低,而且由于使用簡單的無線電接口而存在平安問題.第二代通信系統于20世紀90年代初開始引入,全部使用數字技術.通過在傳輸前將話音波形壓縮使得用戶容量提升了三倍.第三代通信系統是對第二代系統在復雜性方面的擴展,預計于2000年以后啟用.通過使用復雜的復用技術如CDMA或TDMA的擴展,并提升效勞的靈活性使得系統容量比原來的第一代系統提升10倍.Foreachcombinationofcommunication(modulation/detection)type,channelfadingmodel,anddiversitytype,theaveragebiterrorrate(BER)and/orsymbolerrorrate(SER)ofthesystemisobtainedandrepresentedbyanexpressioninaformthatcanreadilybeevaluated.Allcasesconsideredcorrespondtorealpracticalchannels,andinmanyinstancestheBERandSERexpressionsobtainedcanbeevaluatednumericallyonahand-heldcalculator.對于通信(調制/檢測)類型、信道衰落模型、分集類型的每一種組合,得到系統的平均誤碼率(BER)和符號錯誤率(SER),并以容易求值的形式表示.所有考慮的相應于實際信道的情況,以及許多情況下得到的BER和SER表達式均可用手持計算器來計算.Modulationisthesystematicvariationofsomeattributeofacarrierwaveformsuchastheamplitude,phase,orfrequencyinaccordancewithafunctionofthemessagesignal.Itisusedincommunicationsystemsformatchingsignalcharacteristicstochannelcharacteristics,forreducingnoiseandinterference,forsimultaneouslytransmittingseveralsignalsoverasinglechannel,andforovercomingsomeequipmentlimitations.Aconsiderableportionofthisbookisdevotedtothestudyofhowmodulationschemesaredeignedtoachievetheabovetasks.Thesuccessofacommunicationsystemdependstoalargeextentonthemodulation.調制是載波波形的某些屬性,例如幅度、相位和頻率,根據消息信號的函數有規那么的變化.它用于通信系統以使信號特性匹配信道特性,減少噪聲和干擾,在單個信道上同時傳輸多個信號,并克服某些設備的限制.本書相當大局部內容是研究如何設計調制方案以實現上述任務.一個通信系統的成功很大程度上依賴于調制.Unit5Exercises⑴TranslatethefollowingpassageintoChinese.OFDMconsistsofalargenumberofsubcarriersequallyspacedinafrequencyband,eachmaybedigitallymodulatedbyasameschemesuchasPSK,QAM,etc.,orbydifferentschemes.Aseriallytransmittedsequenceisdividedintoanumberofsections,eachhavingNsymbols,andtheNsymbolsineachsectionareusedtomodulateNcarriersforsimultaneoustransmission.ThereforeOFDMisessentiallyaparallelmodulationsystem.Whenthenumberofsubcarriersissufficientlylarge,thesystemcanresistmultipathinterference.Thisisbecausethat,inthetimedomain,asymboldurationlongerthanthemultipathdelaycanbechosen,whileinthefrequencydomain,eachsymbolonlyoccupiesasmallportionofthechannel'sfrequencyband.Thus,theeffectofmultipathfadingspreadsovermanysymbols,resultinginslightdistortiontomanysymbolsratherthancomplete

destroyofafewsymbols.Inthisway,correctdemodulationisnotaffectedsothatthesignaldestroyofafewsymbols.Inthisway,correctdemodulationisnotaffectedsothatthesignalcanbeaccuratelyrecoveredatthereceiver.InanOFDMsystem,theprincipleofchoosingthesubcarrierintervalistomakethesubcarriersmutuallyorthogonalwithintheentiresymbolperiod.Thus,evenifspectraloverlapexistsbetweenthesubcarriers,thesymbolscanstillberecoveredwithoutloss.Inordertorealizemaximumspectralefficiency,theintervalbetweensubcarriersisusuallychosentoequalthereciprocalofthesymboldurationT.Thereforethesubcarrierfrequenciesinthebasebandarefn=n/T,(n=0,1,...,N1).Denotingthen-thmodulatingN1x(t)X(n)expn0T/NyieldsN1x(k)X(n)expn0j2kT1T/NyieldsN1x(k)X(n)expn0j2kT1nkX(n)exoj2一,k1,2,0N(2)Itisobservedfromtheaboveexpressionthatx(k)andX(n)formadiscreteFouriertransformpair,thereforethebasebandOFDMwaveformcanbegeneratedfromthediscreteFouFouriertransformofNmodulatingsymbols.WhenN=2mwheremisaninteger,thefastalgorithmofIDFTiseasytoimplement.OFDM由大量在頻率上等間隔的子載波構成.每個子載波可用同樣的方案,如PSK,QAM等,或者用不同的方案數字調制.將串行傳輸的符號序列分成許多段,每一段有N個符號,每段的N個符號被用來分別調制N個載波同時發送.因此,OFDM本質上是一個并行調制系統,當載波數足夠大時,這種系統具有抗多徑干擾的水平.這是由于在時域上符號周期能選取得比多徑延遲時間長,而在頻域上每個符號只占整個信道帶寬的一小局部,因此多徑衰落的影響被分散到許多符號上,其結果是許多

符號都發生輕度的畸變,而不是使某些符號被完全破壞.這樣,不影響正確的解調,信號能在接收器中準確地恢復.在OFDM系統中,選擇子載波間隔的原那么是使子載波在整個符號周期內相互正交,這樣.即使在為了實現最大的頻譜效率,子載波之間的間隔子載波間為了實現最大的頻譜效率,子載波之間的間隔通常通常選取為符號周期的倒數.因此基帶子載波頻率為fn=n/T,(n=0,1,...,N1),第n個調制符號記為X(n),在一個符號記為X(n),在一個符號周期內的OFDM波形可表示:x(t)nX(n)exoj27t,在t=T/N時刻采樣這個波形得到:x(k)N1kTn0X(n)ex°j2NN1X(n)expn0nkj2Nk1,2,,N1(2)從上從上面的表示中可以看到,x(k)N個調制符號的離散傅里葉變換來生成.和X(n)構成了一對離散傅里葉變換,因此基帶OFDM波形可根據當N=2m,其中m為整數,IDFT的快速算法很容易實現.Unit6ExercisesTranslatethefollowingsentencesintoChinese.Communicationisthetransmissionofinformationfromonepointtoanother.Thistransmissionrequirestheabilitytovarysignalswithtimeinamannerwhichisunpredictabletothereceiver.通信就是信息從一點傳送到另一點.這種傳送要求信號隨時間發生的變化不能在接收端預測.Itistrueofanycommunicationsystemthattheshapeandamplitudeofthetransmittedsignalwillbecontinuouslydegradedbytheintroductionofnoise,andtheattenuationalongthetransmissionpath.傳輸的信號會不斷地被噪聲的引入和線路上的衰減所損傷,對任何通信系統都是如此.Sincetheverybeginning,communicationssystemshaveconsistedofthreemajorparts,namely,theequipment,themedium,andtheprotocol.Itisstillthecasetoday.However,thecloselinkoftelecommunicationswiththecomputertechnologyhasbroughtabouttremendouschangesincommunications,fromtheconcepts,tothecontentsandthemethods.從一開始通信系統就由設備、媒介和協議三個要素組成.至今依然如此.然算機技術的緊密聯系使得通信從概念到內容和手段都發生了重大的變化.Theavailabilityofsuchalargecollectionofsystemperformancecurvesinasinglecompilationallowstheresearcherorsystemdesignertoperformtrade-offstudiesamongthevariouscommunicationtype/fadingchannel/diversitycombinationssoastodeterminetheoptimumchoiceinthefaceofhisorheravailableconstraints.在一本書中提供如此大量的系統性能曲線,使研究者或系統設計者能在各種通信類型、衰落信道、分集組合之間進行比擬研究,從而在他或她所面臨的限制之下做出最正確的選擇.Thechannelprovidestheelectricalconnectionbetweentheinformationsourceandtheuser.Thechannelcanhavemanydifferentformssuchasamicrowaveradiolinkoverfreespace,apairofwires,oranopticalfiber.信道提供信息源和用戶之間的電路聯接.信道可以有許多不同的形式,比方自由空間里的微波聯接,一對電線,或者一根光纖.Thedegradationofthetransmittedsignalisaresultofsignaldistortionduetoimperfectresponseofthechannelandduetoundesirableelectricalsignals(noise)andinterference.Noiseandsignaldistortionaretwobasicproblemsofelectricalcommunication.傳輸信號的退化是信號失真的結果,而這種失真又是由信道的非理想響應及不想要的電信號〔噪聲〕和干擾引起的.噪聲和信號畸變是電子通信的兩個根本問題.Unit8ExercisesTranslatethefollowingsentencesintoChinese.Earlyinthetwentiethcentury,itwasfoundthatlightcouldcauseatomstoemitelectronsandthat,whenlightreleasedanelectronfromanatom,theenergypossessedbytheelectronverygreatlyexceededthatwhichtheatomcould,accordingtotheelectromagneticwavetheory,havereceived.在二十世紀早期,人們發現光能夠使原子放出電子,而且當光從原子中釋放一個電子時,電子所包含的能量大大超過由電磁波理論得到的原子所接收的能量.Pulsebroadeningdeterminestheminimumseparationbetweenadjacentpulses,whichinturndeterminesthemaximuminformation-carryingcapacityoftheopticalfiber.脈沖的展寬決定了相鄰脈沖之間的最小間隔,這一間隔進而又決定了光纖的最大信息容量.Ifoneweretotransmitsuchinformationwithoutimpressingitonanopticalcarrierbutinsteadonaradiofrequency(RF)carrierabithigherthanthemaximumrate,thetransmissionwavelengthoftheRFcarrierwouldbecentimetersorlarger.如果傳輸這樣的信息不是將它加載到光纖上,而是加載在略高于最大速率的射頻載波上,那么此射頻載波就會是厘米波或是波長更長一些的波.Thesmallnessoftheopticalwavelength,therefore,allowsfortheminiaturizationoftransmitandreceivemodules,whichshouldallowconsiderablereductioninsize,weight,andcostofopticalcommunicationsystemswithrespecttomicrowave/radiowavecounterparts.光波波長之小使發射和接收模塊得以小型化,這就使光通信系統的尺寸、重量以至價格與相應的微波、無線電波通信系統相比都大為降低.Althoughalltheadvantagesofcoherentopticalcommunicationsystemshaveyettobebroughttofruition,anotherpropertyofopticalradiationhasmadetoday'sopticalcommunicationsystemsnotdesirableforapplications.雖然相干光通信系統的所有優點還有待于落實在具體成果中,光輻射的另一性質卻使目前的光通信系統不利于應用.Whencoupledwithlight'sshortwavelengthwhichallowsforminiaturesourcesanddetectorsandmicron-sizedwaveguides,directdetectionschemeshaveallowedforsmall,lightweight,highbandwidthsystemswhicharecompetitiveinmanyareas,mostnotablytothepresenttelecommunicationstransmission,althoughamyriadofotherapplicationsarecontinuallyopeningup.光的波長很小,可以使用小型的光源和檢測器以及微米級的波導,于是用直接檢測方案可實現在許多領域具有競爭力的小巧的寬帶系統,這些領域中特別引人注目的是當前電信傳輸中的應用,盡管無數其他應用也在不斷涌現出來.Asmentionedpreviously,theseapplicationshavetendedtoopenupmoreslowlythanoriginallypredicted,ascostwasreallynotmuchofaconsiderationintelecommunications,whereequipmentcostsareswampedbyotherconsiderations.如前所述,〔線路〕本錢并非電信系統中真正重要的考慮因素,通信設備的本錢主要受到其他因素的制約,因此這些應用比預料的出現得慢.Aswavelengthsdecreasetoapproachthesizeofcircuitcomponents,circuitelementsarenolongerlumpedassuch,andleadscanactasreflectivecomponentsand/orantennasandlumpedelementsaselectromagneticresonators.隨著波長減小到接近于電路元件的尺寸,電路單元就不再是集總的,導線可起到反射元件以及〔或〕天線的作用,集總單元那么成為電磁諧振器.Unit11ExercisesInatelevisionscanninggeneratorusingapairoffree-runningrelaxationoscillators,free-runningfrequenciesoftheoscillatorsaresetslightlybelowthehorizontalandverticalpulserates,andthestrippedpulsesareusedtotriggertheoscillatorsprematurelyandthustosynchronizethemtothelineandhalf-framerates.在采用一對自由張弛振蕩器的電視掃描發生器中,振蕩器的自由頻率被設置得略低于水平和垂直〔掃描〕頻率,別離出來的脈沖被用來提前觸發振蕩器從而使它們與行頻和半幀頻〔場頻〕同步.Unit12ExercisesReferringtothefigure,weseethatsignalprocessingtechniquesareneededforpreprocessing,patternrecognitiontechniquesareneededforsegmentation,featureextraction,andclassification,andartificialintelligencetechniquesareneededforstructureanalysis,knowledge-acquisitionandrepresentation〔worldmodel〕,andcontrolstructure〔interactionamongtheblocks〕.參考圖,我們看到信號處理技術是預處理所需要的,模式識別技術是分割、特征提取以及分類所需要的,而人工智能技術那么是結構分析、知識獲取及表示〔世界模型〕以及限制結構〔塊間交互〕所需要的.Thepictureelementsacrossalineareconvertedtothevideosignalandlow-passfilteredwithanelectricalfilter.Thissmoothingremovesthediscretestructureinthehorizontaldimension.沿著一條直線的圖像像素被轉換成視頻信號,然后由一個電子濾波器進行低通濾波.這一平滑處理可消除水平方向的離散結構.Unit13ExercisesTranslatethefollowingsentencesintoChinese.Theprecedingchaptershavedescribedhowtheautomaticcomputerperforms,buthavenotdescribedhowtheautomaticcomputercanbeputtousetododatahandlingworktoserveanorganization,norwhysuchworkisdoneinthewaythatitis.前面的章節講述了自動計算機是如何工作的,但沒有講述自動計算機如何能用于數據處理工作以效勞于一個機構,也沒有講述這種工作為什么用這種方法實現.Whilethesubjectofcodingoftencarrieswithitanairofsecrecy,amoreimportantmotiveinmanycodingsystemsistheimprovedefficiencyinconveyinginformation.如果說編碼這一主題常帶有一種秘密的色彩,那么許多編碼系統的一個更重要的目的那么是為了提升信息傳遞的效率.Unit14Exercises(1)TranslatethefollowingsentencesintoChinese.1.Theimportanceofearlybraindevelopmentinsettingthefoundationsforlanguageisapparentinbabiesyoungerthan6months.大腦的早期開展對于奠定語言根底的重要性在六個月以下的嬰兒中是顯而易見的.Unit15ExercisesTranslatethefollowingpassageintoChinese.Becausedigitalimageprocessingdoesencompasssuchawidevarietyoftechniquesandmathematicaltools,eachapplicationinvolvesasequenceofprocessingsteps.Thesestepsaremodulesthatcanbearrangedinanenormousnumberofdifferentsequences,andeachmodulegenerallyadmitsthespecificationofparametervaluesthatfurtherexpandtherangeofpossiblemanipulationschemestoachievethedesiredresults.Themajoradvantagesofdigitalimagesascomparedwithanalog(i.e.film)imagesarethequalityofthedataandtheaccessibilityofthatdatatocomputermanipulation.Thequalityadvantageisreallyanaggregateoftwoadvantages:Dynamicrange:upto128ormoregraylevelscanbepresentondigitalimageswhereasonly1530discernibleonfilmproducts.Reproducibility:acopyofacopyofacopyofadigitalimagecontainsexactlythesamedataastheoriginal,whereasaforth-generationphotographicproductissubstantiallydegradedincomparisonwiththeoriginal.Althoughtheseareadvantages,thecompellingadvantagefortheapplicationscommunityderivesfromtheaccessibilityofthedatatocomputermanipulation.Togenerateageneral-purposefilmproductisessentiallytochooseacompromiseamongcompetingrequirementsfromagronomists,hydrologists,foresters,geologists,urbanplanners,andotherusergroups;itisnotoptimizedforanyone.Digitalimageslendthemselvestocustomtailoringbytheuserforhisorherapplicationinawaythatfilmproductscannot.數字圖數字圖像處理包括了多種多樣的技術和數學工具,每一項應用都涉及到一系列的處理步驟.這些步驟是以大量不同次序排列的各種模塊,每一模塊通常容許一些參數值的技術指標,從而進一步擴大了為獲得預期結果而可能采取的處理方案的選擇范圍.與模擬圖像(即膠片)相比,數字圖像的主要優點在于數據的質量和數據可供計算機進行處理這兩方面.質量方面的優越性實際上是以下兩種優越性的綜合：動態范圍：數字圖像可表現128級或更多的灰度,而膠片產品只能分辨15至30級；重現性：一幅數字圖像屢次復制后仍與原件包含完全相同的信息,而一幅第四代的照片與原件相比卻大大地退化(損傷)了.Unit16ExercisesTranslatethefollowingsentencesintoChinese.Inrecentyears,therehasbeenatremendousincreaseintheuseofdigitalcomputersandspecial-purposedigitalcircuitryforperformingvariedsignalprocessingfunctionsthatwereoriginallyachievedwithanalogequipment.近年來為實現各種信號處理功能,數字計算機和專用數字電路的使用有了巨大的增長,這些處理功能原先都是用模擬設備實現的.Inthebeginning,computerswereusedtoprocessonlynumericalinformation,butmajorityofourinformationisnon-numericalinnatureandverylittleisknownaboutitsdescriptionandprocessing.一開始計算機只是被用來處理數值信息,而我們的大多數信息都是非數值性質的,而且人們對這些信息的描述和處理所知甚少.Unit17ExercisesTranslatethefollowingpassagesintoChinese.Forthefirsttimeeverthelandscapeischanging,ashighvolumepersonalcomputermultimediaapplicationsproliferate.Firstaffectedweremonitors,whichfor

sosometimehaveofferedhigher-than-broadcastspeedandresolution.Onecanexpectcamerastofollow,withhigh-speed,high-resolutiondevicesdrivenbyconsumerdigitalstillcameratechnologyandlower-resolution,ultralowcostunitsdrivenbyentertainment,internetconferencing,andperceptualuserinterfaceapplications.隨著大量個人計算機多媒體應用的急劇增加,情況首次發生了變化.最早受到影響的是顯示器,相當長時間以來它已經能夠提供比播送級更高的分辨率和速度.人們可期待照相機/攝像機也隨之跟上,包括由民用數字照相機所推動的高速度、高分辨率器件,娛樂業、互聯網遠程會議和用戶視覺界面應用所推動的低分辨率和極低價格的設備.IfyoualreadyhavethefastestCPUinaparticularfamilyandstillwantmoreperformance,thenitmaybemorecost-effectivetoaddsystemRAMorcacheRAMthantoputinaprocessorfromadifferentfamily.Addingsystemmemorycanbringsignificantperformanceincreasesatarelativelylowcost,assumingyouconfigurethememorycorrectly.InadditiontoaddedcacheandsystemRAM,afasterandlargerharddrivecansaveyoutimewhenrunningapplicationsdependentonheavydriveaccessanddatathroughput.Addingagraphicsacceleratorcardcanhelp,too,especiallyifyouarelookingforawaytostayawakewhileyoursystemredrawsimages.如果你已經有了某一系列中最快的CPU而還想要更多的性能,那么增加系統RAM或高速緩存RAM也許比插入一枚另一系列的處理器更合算.特別是如果彳是一名Windows用戶,假設你正確地配置內存,那么增加系統內存可以較低的代價帶來可觀的性能提升.除了增加高速緩存或系統RAM,一個更快和更大的硬盤可在運行依賴于大量讀寫硬盤和有大量數據吞吐時節省你的時間.增加一個圖形加速器也是有益的,如果你使用Windows,而且發現你在尋找某種途徑使你在系統重顯圖象時能保持“清醒〞,那么尤其是如此.

3.Inuniversityenvironments,MATLABhasbecomethestandardinstructionaltoo3.forintroductorycoursesinappliedlinearalgebra,aswellasadvancedcoursesinotherareas.Inindustrialsettings,MATLABisusedforresearchandtosolvepracticalengineeringandmathematicalproblems.Typicalusesincludegeneralpurposenumericalcomputation,algorithmprototyping,andspecialpurposeproblemsolvingwithmatrixformulationsthatariseindisciplinessuchasautomaticcontroltheory,statistics,anddigitalsignalprocessing(time-seriesanalysis).在大學環境里,它已成為應用線性代數導論以及其他領域中許多高級課程的標準教學工具.在工業界,MATLAB被用于研究和解決實際的工程和數學問題.典型的應用包括通用數值計算、算法原型測試以及使用矩陣公式的專門問題的解決,這些問題是在自動限制理論、統計、數字信號處理(時間序列分析)等學科中提出來的.Multimediaisagenerictermformultimediacomputing“orinteractivemultimedia〞.Thecomputerandsoftwareareusedtocontrolandnavigatethroughthecommunicationslinks,notonlyoneatthetime,butseveralsimultaneously.Computersystemshavebeenmostdevelopedinusingvisionandhearingtointerfacebetweenthedigitalandanalogueworlds,e.g.,stillandmovingimages,textandgraphicsusethevisualsenses,andaudiouseshearing.Multimediaisdefinedasvisual,audioandtextualinformationwhichcanbepresented,separatelyorsimultaneously,toconveyandpresentinformationinteractivelytousers.Itistechnicallyeasytodigitizetheanalogueformsofthesecommonmediaandhandledbycomputersnowwidelyavailableandinexpensivetobeaccessibletomostusers.多媒體是表示“多媒體計算〞或“交互式多媒體〞的一般術語.計算機和軟件被用于限制并通過不止

一條通信鏈接同時進行瀏覽.在利用視覺和聽覺在數字和模擬世界之間進行交互方面,計算機系統已得到極大的開展,例如對靜止和活動圖像、文本和圖形使用視覺,對音頻使用聽覺.多媒體被定義為可以分別或同時展現的視頻、音頻、文本信息,用以交互式地將信息傳遞和展示給用戶.技術上很容易將這些普通媒體的模擬形式用計算機實現數字化并加以處理,計算機現在已十分普遍,其價格廉價,大多數用戶都能使用.Theessentialcapabilityofanymultimediacomputersystemistheabilitytoconverttheanaloguesignaltoadigitalformatandtocompressthisinformationusingstandardalgorithms.ThepoweroftheCPUwilldeterminewhetherthisprocesscanbecarriedoutinreal-timeorwhetherithastobedoneoff-line.OriginallythispoweronlyexistedinUNIXsystems,butmorerecentlyithasbecomeavailableinPCsandMacintosh.Thecompressionprocessisnecessaryotherwisethequantityofdatatobestoredandtransmittedwouldbeexcessive.MostPCshaveuntilrecentlydependeduponhardwareencoding/decodingsystems,butthespeedofcurrentprocessorsissuchthatsoftwarecompressionsystemshavebeendeveloped.Theadvantageofthesoftwaresystemsisthatthecompatibilityandinteroperabilityissuescanbehandledmoreeasily,andthecostoftheequipmentisnotraisedbytheneedtopurchaseexpensivehardwaredevices.任何多媒體計算機的根本功能是將模擬信號轉換成數字格式,并用標準算法將此信息壓縮的水平.CPU處理水平將決定是否能實時完成此過程還是必須離線執行.原先只有UNIX系統才有這種實時而且不會因購置水平,但近年來PC和Macintosh也能勝任〔有這種水平〕了.壓縮是必須的,否那么要存儲和傳送的數據量太大.直到不久前大多數PC還依賴硬件編解碼系統,而目前的處理器速度已使軟件編解碼系統的開發成為可能.軟件系統的優點在于可更方便地處理兼容性和協而且不會因購置昂貴的硬件而提升設備本錢.Unit19ExercisesTranslatethefollowingparagraphsintoChinese.ArtificialIntelligenceisabranchofsciencethathelpsmachinesfindsolutionstocomplexproblemsinahuman-likefashion.Thisgenerallyinvolvesborrowingcharacteristicsfromhumanintelligence,andapplyingthemasalgorithmsinacomputerfriendlyway.Computersarefundamentallywellsuitedtoperformingmechanicalcomputationsusingfixedrules.Thisallowsmachinestoperformsimplemonotonoustasksefficientlyandreliably,whichhumansarenotsuitedto.Unlikehumans,however,computershavetroubleinunderstandingspecificsituations,andadaptingtonewsituations.ArtificialIntelligenceaimstoimprovemachinebehaviorintacklingsuchcomplextasks.Humanshaveaninterestingapproachtoproblem-solving,basedonabstractthought,high-levelreasoningandpatternrecognition.ArtificialIntelligencecanhelpusunderstandthisprocessbyrecreatingit,thenpotentiallyenablingustoenhanceitbeyondourcurrentcapabilities.人工智能是一個科學分支,它可以幫助機器找到像人那樣解決復雜問題的解.這通常包括從人的智能中借用一些特征,應用這些特征開發出便于計算機實現的算法.計算機原那么上適合于根據固定的編程規那么進行機械性的計算,這使得機器能夠有效而可靠地執行簡單單調的任務,這正是人所不擅長的.然而不同于人,計算機難以理解特定的情形,適應的新情況.人工智能的目標就是改良機器的性能以對付這種復雜的任務.人類具有一種解決問題的有趣水平,這種水平是基于抽象思維、高級推理和模式識別的.人工智能可以通過重建這一過程來幫助我們理解它,進而使我們的水平有可能超越當前的水平.Itisrarethattheoptimizationwill