信息科学和电子工程专业英语课后翻译答案解析

Unit1ExercisesTranslatethefollowingsentencesintoChinese.Aswithseriesresonance,thegreatertheresistanceinthecircuitthelowertheQand,accordingly,theflatterandbroadertheresonancecurveofeitherlinecurrentorcircuitimpedance.对于串联谐振,电路中的电阻愈大Q值就愈低,相应地线路电流或电路阻抗的谐振曲线也就愈平、愈宽.Awirecarryingacurrentlooksexactlythesameandweighsexactlythesameasitdoeswhenitisnotcarryingacurrent.一根带电的导线其外表与重量都与不带电导线完全一样.Clickmouseonthewaveformanddragittochangethepulserepetitionrate,ordirectlyenteranewvalueoftheperiodintheprovideddialoguebox,whilekeepingthepulsewidthunchanged.在波形上点击鼠标并拖动来改变脉冲重复频率,或者在提供的对话框中直接输入新的周期值,而保持脉冲宽度不变.Electronicsisthescienceandthetechnologyofthepassageofchargedparticlesinagas,inavacuum,orinasemiconductor.Pleasenotethatparticlemotionconfinedwithinametalonlyisnotconsideredelectronics.电子学是一门有关带电粒子在气体、真空或半导体中运动的科学技术.注意,在本书中粒子运动仅限于金属的情况不属于电子学.Hardwaretechnologieshaveplayedvitalrolesinourabilitytouseelectronicpropertiestoprocessinformation,butsoftwareanddataprocessingaspectshavenotdevelopedatthesamespeed.硬件技术在我们使用电子特性来处理信息的水平中一直起着重要作用,而软件及数字处理方面却没能与硬件同步开展.However,inaproperlydesignedDCamplifiertheeffectoftransistorparametervariation,otherthanIco,maybepracticallyeliminatediftheoperationpointofeachstageisadjustedsothatitremainsinthelinearoperationrangeofthetransistorastemperaturevaries.然而在设计得当的直流放大器中,假设调节每一级的工作点使之在温度变化时保持在晶体管线性区,就能在实际上消除Ico以外的晶体管参数变化所造成的影响.Unit2Exercises⑴TranslatethefollowingsentencesintoChinese.Ifanalogsignalsaretobetransmitteddigitally,theyfirsthavetobesampledataspecifiedrateandfurtherconvertedtodiscreteamplitudesamplesbyquantization.如果要以数字方式传输模拟信号,首先必须以一定的频率对信号进行采样,然后通过量化进一步将它们转换为离散的幅度样本.Linearfiltersamplifyorattenuateselectedspatialfrequencies,canachievesucheffectsassmoothingandsharpening,andusuallyformthebasisofre-samplingandboundarydetectionalgorithms.线性滤波器放大或衰减选择的空间频率,能够实现像平滑和锐化这些效果,通常是重采样和边缘检测算法的根底.Stabilityandrepeatabilityarefundamentalattributesofdigitalcircuits,however,andthenecessaryaccuracycanbeobtainedinadigitalversionofthemodulatorbyanappropriatechoiceofwordlengthtorepresentthesignals.不过稳定性和可重复性是数字电路的根本性质,在数字式调制器中必要的精度可通过适当地选择代表信号的字长而获得.Thefirstobservationismadeonthefundamentalrelationshipbetweenthenatureofsystemandtheperiodicityofitsfrequencyresponse:acontinuoussystemhasanaperiodicfrequencyresponse,whileadiscretesystemhasaperiodicfrequencyresponse.从系统性质和它频率响应的周期性之间的根本关系中首先可以看到：连续系统有非周期性的频率响应,而离散系统有周期性的频率响应.Themainfunctionofthereceiveristoextracttheinputmessagesignalfromthedegradedversionofthetransmittedsignalcomingfromthechannel.接收器的主要功能是从由信道传输来的退化了的信号中提取出输入消息.Unit3Exercises⑴TranslatethefollowingsentencesintoChinese.Averycommonlyusedmethodofmicrowavemeasurementsisbasedonthestudyofastandingwavepatternformedalongthelinebecauseoftheinterferenceofincidentandreflectedwaves.一个很常用的微波测量方法是基于对驻波图型的研究,这种驻波是由入射波和反射波之间的干预而沿着传输线形成的.Computationsshowareductionof6dBintheEMfieldintensitywiththedistancedoubled,andanincreaseof3dBintheintensitywiththetransmittedpowerdoubled.Thisresultprovidesverificationtothealgorithmused.计算说明,当距离增大一倍时,电磁场强度减小6分贝；而发射功率增大一倍时,场强那么增加贝.这一结果验证了所用算法的正确性.Liketransferofheatbyconduction,convectionandradiation,microwaveheatingcanbeconsideredasanothermodeofheattransfer,inwhichheatisproduceddirectlyatthelocationofthedielectriclosses.就像通过传导、对流、辐射来传递热量一样,微波加热可以看作热传递的另一种方式,即热量直接产生于发生介电损耗的地方.Operationoftheradarisbasedonthemeasurementofthetimeittakesforapulsetransmittedfromanantennatogetreflectedbytheobjecttobedetectedandtoreturnattheantennaandthereceiver.雷达的工作是基于对天线发出的脉冲被所要探测的目标反射,〔然后〕回到天线和接收机所需时间的测量.OthermotivationsforusingCADincircuitdesignincludesthewishtoacquireconfidenceinadesignthatwasaccomplishedbyothermeans,and,notleastinimportance,asenseofcuriosityorperhapsadesiretodiscovertheunexpected.在电路设计中使用CAD的其它动机包括：想要验证用别的方法设计出来的电路；满足好奇心或者可能是想发现预想不到的现象.后一个动机并非是最不重要的.〔取得信心,并非最不重要,意料之外的事〕Thespacingbetweentherepeatingamplifiersisafunctionofthecableattenuationandthesystembandwidthsothatthegainprovidedbytheseamplifierscompensatesforthelossintroducedbythecable.中继放大器之间的间距是电缆衰减和系统带宽的函数,以便这些放大器提供的增益补偿电缆引起的损耗.Whenthecut-offfrequencyisnolessthanthemaximalfrequencyoftheoriginalsignal,norisitgreaterthanthedifferencebetweenthesamplingfrequencyandthemaximalfrequency,theoriginalsignalmaybecompletelyrebuilt.当截止频率不小于原始信号的最高频率,也不大于采样频率和最高频率之差,原始信号可以完整地重建.WhilethepoliticsofthelastonehundredyearscenteredaroundIndustrialAgetechnology,thepoliticsofthefuturewillbebasedonInformationAgeconcernsorientedtowardsthestorage,protectionandexchangeofinformation.尽管近百年来的政治活动是以工业时代的技术为中央的,未来的政治活动将基于信息时代的事物,面向信息的存储、保护和交换.Unit4Exercises⑴TranslatethefollowingpassagesintoChinese.Communicationmaybebroadlydefinedasthetransferofinformationfromonepointtoanother.Whentheinformationistobeconveyedoveranydistanceacommunicationsystemisusuallyrequired.Withinacommunicationsystemtheinformationtransferisfrequentlyachievedbysuperimposingormodulatingtheinformationontoanelectromagneticwavewhichactsasacarrierfortheinformationsignal.Thismodulatedcarrieristhentransmittedtotherequireddestinationwhereitisreceivedandtheoriginalinformationsignalisobtainedbydemodulation.Sophisticatedtechniqueshavebeendevelopedforthisprocessbyusingelectromagneticcarrierwavesoperatingatradiofrequenciesaswellasmicrowaveandmillimeterwavefrequencies.

However,communicationmayalsobeachievedbyusinganelectromagneticcarrierthatisselectedfromtheopticalrangeoffrequencies.通信可以广义地定义为从一处到另一处的信息传递.当要将信息传输到任何距离以外时就需要有一个通信系统.在通信系统内部,信息的传输经常通过将信息叠加或调制到作为信号载体的电磁波上来实现.经调制的载波然后被传送到要求的目的地,在那里被接收,原始信号通过解调被恢复出来.为了实现这一过程,已经利用工作在射频、微波以及毫米波频率上的电磁载波开发了复杂的技术.不过通信也可以用光波频段上的电磁载波来实现.Electroniccommunicationsisthetransferandmovementofdatabetweenlocationsthroughtheuseofcomputers.Anelectroniccommunicationsystemincludestheequipmentneededtosupportthemovementofinformation,thecommunicationlinesandmediatocarrytheinformation,thecomputersoftwareandprogramstocontroltheflowofinformation,thepersonneltoplan,implement,andoperatecommunications,andthemanagementofalltheseresources.Electroniccommunicationsestablisheslinksbetweenpeopleaswellascomputers.电子通信就是通过使用计算机在不同的地点之间传输数据.一个电子通信系统包括：支持信息流动所需要的设备,承载信息的通信线路和媒介,限制信息流的计算机软件和程序,方案、实施、操作通信系统的人员,以及对所有这些资源的治理.电子通信建立起人和人、计算机和计算机之间的联系.Firstgenerationcommunicationssystemscanbecharacterizedbytheuseofanalogtransmissiontechniques,andtheuseofsimplemultiplexaccesstechniquessuchasfrequencydivisionmultipleaccess(FDMA).Theysufferedfromalowusercapacity,andintroducedintheearly1990securityproblemsduetothesimpleradiointerfaceused.Secintroducedintheearly1990's,andallusedigitaltechnology.Thisprovidedanincreaseintheusercapacityofaroundthreetimes,achievedbycompressingthevoicewaveformsbeforetransmission.Thirdgenerationsystemsareanextensiononthecomplexityofsecond-generationsystemsandaretobeintroducedaftertheyear2000.Thesystemcapacitywillbeincreasedtoovertentimesoriginalfirstgenerationsystems,achievedbyusingcomplexmultiplexaccesstechniquessuchascodedivisionmultiplexaccess(CDMA),oranextensionofTDMA,andbyimprovingflexibilityofservicesavailable.第一代通信系统以模拟传输技术和简单复用技术如频分复用为特征.这些系统用户容量低,而且由于使用简单的无线电接口而存在平安问题.第二代通信系统于20世纪90年代初开始引入,全部使用数字技术.通过在传输前将话音波形压缩使得用户容量提升了三倍.第三代通信系统是对第二代系统在复杂性方面的扩展,预计于2000年以后启用.通过使用复杂的复用技术如CDMA或TDMA的扩展,并提升效劳的灵活性使得系统容量比原来的第一代系统提升10倍.Foreachcombinationofcommunication(modulation/detection)type,channelfadingmodel,anddiversitytype,theaveragebiterrorrate(BER)and/orsymbolerrorrate(SER)ofthesystemisobtainedandrepresentedbyanexpressioninaformthatcanreadilybeevaluated.Allcasesconsideredcorrespondtorealpracticalchannels,andinmanyinstancestheBERandSERexpressionsobtainedcanbeevaluatednumericallyonahand-heldcalculator.对于通信(调制/检测)类型、信道衰落模型、分集类型的每一种组合,得到系统的平均误码率(BER)和符号错误率(SER),并以容易求值的形式表示.所有考虑的相应于实际信道的情况,以及许多情况下得到的BER和SER表达式均可用手持计算器来计算.Modulationisthesystematicvariationofsomeattributeofacarrierwaveformsuchastheamplitude,phase,orfrequencyinaccordancewithafunctionofthemessagesignal.Itisusedincommunicationsystemsformatchingsignalcharacteristicstochannelcharacteristics,forreducingnoiseandinterference,forsimultaneouslytransmittingseveralsignalsoverasinglechannel,andforovercomingsomeequipmentlimitations.Aconsiderableportionofthisbookisdevotedtothestudyofhowmodulationschemesaredeignedtoachievetheabovetasks.Thesuccessofacommunicationsystemdependstoalargeextentonthemodulation.调制是载波波形的某些属性,例如幅度、相位和频率,根据消息信号的函数有规那么的变化.它用于通信系统以使信号特性匹配信道特性,减少噪声和干扰,在单个信道上同时传输多个信号,并克服某些设备的限制.本书相当大局部内容是研究如何设计调制方案以实现上述任务.一个通信系统的成功很大程度上依赖于调制.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由大量在频率上等间隔的子载波构成.每个子载波可用同样的方案,如PSK,QAM等,或者用不同的方案数字调制.将串行传输的符号序列分成许多段,每一段有N个符号,每段的N个符号被用来分别调制N个载波同时发送.因此,OFDM本质上是一个并行调制系统,当载波数足够大时,这种系统具有抗多径干扰的水平.这是由于在时域上符号周期能选取得比多径延迟时间长,而在频域上每个符号只占整个信道带宽的一小局部,因此多径衰落的影响被分散到许多符号上,其结果是许多

符号都发生轻度的畸变,而不是使某些符号被完全破坏.这样,不影响正确的解调,信号能在接收器中准确地恢复.在OFDM系统中,选择子载波间隔的原那么是使子载波在整个符号周期内相互正交,这样.即使在为了实现最大的频谱效率,子载波之间的间隔子载波间为了实现最大的频谱效率,子载波之间的间隔通常通常选取为符号周期的倒数.因此基带子载波频率为fn=n/T,(n=0,1,...,N1),第n个调制符号记为X(n),在一个符号记为X(n),在一个符号周期内的OFDM波形可表示:x(t)nX(n)exoj27t,在t=T/N时刻采样这个波形得到:x(k)N1kTn0X(n)ex°j2NN1X(n)expn0nkj2Nk1,2,,N1(2)从上从上面的表示中可以看到,x(k)N个调制符号的离散傅里叶变换来生成.和X(n)构成了一对离散傅里叶变换,因此基带OFDM波形可根据当N=2m,其中m为整数,IDFT的快速算法很容易实现.Unit6ExercisesTranslatethefollowingsentencesintoChinese.Communicationisthetransmissionofinformationfromonepointtoanother.Thistransmissionrequirestheabilitytovarysignalswithtimeinamannerwhichisunpredictabletothereceiver.通信就是信息从一点传送到另一点.这种传送要求信号随时间发生的变化不能在接收端预测.Itistrueofanycommunicationsystemthattheshapeandamplitudeofthetransmittedsignalwillbecontinuouslydegradedbytheintroductionofnoise,andtheattenuationalongthetransmissionpath.传输的信号会不断地被噪声的引入和线路上的衰减所损伤,对任何通信系统都是如此.Sincetheverybeginning,communicationssystemshaveconsistedofthreemajorparts,namely,theequipment,themedium,andtheprotocol.Itisstillthecasetoday.However,thecloselinkoftelecommunicationswiththecomputertechnologyhasbroughtabouttremendouschangesincommunications,fromtheconcepts,tothecontentsandthemethods.从一开始通信系统就由设备、媒介和协议三个要素组成.至今依然如此.然算机技术的紧密联系使得通信从概念到内容和手段都发生了重大的变化.Theavailabilityofsuchalargecollectionofsystemperformancecurvesinasinglecompilationallowstheresearcherorsystemdesignertoperformtrade-offstudiesamongthevariouscommunicationtype/fadingchannel/diversitycombinationssoastodeterminetheoptimumchoiceinthefaceofhisorheravailableconstraints.在一本书中提供如此大量的系统性能曲线,使研究者或系统设计者能在各种通信类型、衰落信道、分集组合之间进行比拟研究,从而在他或她所面临的限制之下做出最正确的选择.Thechannelprovidestheelectricalconnectionbetweentheinformationsourceandtheuser.Thechannelcanhavemanydifferentformssuchasamicrowaveradiolinkoverfreespace,apairofwires,oranopticalfiber.信道提供信息源和用户之间的电路联接.信道可以有许多不同的形式,比方自由空间里的微波联接,一对电线,或者一根光纤.Thedegradationofthetransmittedsignalisaresultofsignaldistortionduetoimperfectresponseofthechannelandduetoundesirableelectricalsignals(noise)andinterference.Noiseandsignaldistortionaretwobasicproblemsofelectricalcommunication.传输信号的退化是信号失真的结果,而这种失真又是由信道的非理想响应及不想要的电信号〔噪声〕和干扰引起的.噪声和信号畸变是电子通信的两个根本问题.Unit8ExercisesTranslatethefollowingsentencesintoChinese.Earlyinthetwentiethcentury,itwasfoundthatlightcouldcauseatomstoemitelectronsandthat,whenlightreleasedanelectronfromanatom,theenergypossessedbytheelectronverygreatlyexceededthatwhichtheatomcould,accordingtotheelectromagneticwavetheory,havereceived.在二十世纪早期,人们发现光能够使原子放出电子,而且当光从原子中释放一个电子时,电子所包含的能量大大超过由电磁波理论得到的原子所接收的能量.Pulsebroadeningdeterminestheminimumseparationbetweenadjacentpulses,whichinturndeterminesthemaximuminformation-carryingcapacityoftheopticalfiber.脉冲的展宽决定了相邻脉冲之间的最小间隔,这一间隔进而又决定了光纤的最大信息容量.Ifoneweretotransmitsuchinformationwithoutimpressingitonanopticalcarrierbutinsteadonaradiofrequency(RF)carrierabithigherthanthemaximumrate,thetransmissionwavelengthoftheRFcarrierwouldbecentimetersorlarger.如果传输这样的信息不是将它加载到光纤上,而是加载在略高于最大速率的射频载波上,那么此射频载波就会是厘米波或是波长更长一些的波.Thesmallnessoftheopticalwavelength,therefore,allowsfortheminiaturizationoftransmitandreceivemodules,whichshouldallowconsiderablereductioninsize,weight,andcostofopticalcommunicationsystemswithrespecttomicrowave/radiowavecounterparts.光波波长之小使发射和接收模块得以小型化,这就使光通信系统的尺寸、重量以至价格与相应的微波、无线电波通信系统相比都大为降低.Althoughalltheadvantagesofcoherentopticalcommunicationsystemshaveyettobebroughttofruition,anotherpropertyofopticalradiationhasmadetoday'sopticalcommunicationsystemsnotdesirableforapplications.虽然相干光通信系统的所有优点还有待于落实在具体成果中,光辐射的另一性质却使目前的光通信系统不利于应用.Whencoupledwithlight'sshortwavelengthwhichallowsforminiaturesourcesanddetectorsandmicron-sizedwaveguides,directdetectionschemeshaveallowedforsmall,lightweight,highbandwidthsystemswhicharecompetitiveinmanyareas,mostnotablytothepresenttelecommunicationstransmission,althoughamyriadofotherapplicationsarecontinuallyopeningup.光的波长很小,可以使用小型的光源和检测器以及微米级的波导,于是用直接检测方案可实现在许多领域具有竞争力的小巧的宽带系统,这些领域中特别引人注目的是当前电信传输中的应用,尽管无数其他应用也在不断涌现出来.Asmentionedpreviously,theseapplicationshavetendedtoopenupmoreslowlythanoriginallypredicted,ascostwasreallynotmuchofaconsiderationintelecommunications,whereequipmentcostsareswampedbyotherconsiderations.如前所述,〔线路〕本钱并非电信系统中真正重要的考虑因素,通信设备的本钱主要受到其他因素的制约,因此这些应用比预料的出现得慢.Aswavelengthsdecreasetoapproachthesizeofcircuitcomponents,circuitelementsarenolongerlumpedassuch,andleadscanactasreflectivecomponentsand/orantennasandlumpedelementsaselectromagneticresonators.随着波长减小到接近于电路元件的尺寸,电路单元就不再是集总的,导线可起到反射元件以及〔或〕天线的作用,集总单元那么成为电磁谐振器.Unit11ExercisesInatelevisionscanninggeneratorusingapairoffree-runningrelaxationoscillators,free-runningfrequenciesoftheoscillatorsaresetslightlybelowthehorizontalandverticalpulserates,andthestrippedpulsesareusedtotriggertheoscillatorsprematurelyandthustosynchronizethemtothelineandhalf-framerates.在采用一对自由张弛振荡器的电视扫描发生器中,振荡器的自由频率被设置得略低于水平和垂直〔扫描〕频率,别离出来的脉冲被用来提前触发振荡器从而使它们与行频和半帧频〔场频〕同步.Unit12ExercisesReferringtothefigure,weseethatsignalprocessingtechniquesareneededforpreprocessing,patternrecognitiontechniquesareneededforsegmentation,featureextraction,andclassification,andartificialintelligencetechniquesareneededforstructureanalysis,knowledge-acquisitionandrepresentation〔worldmodel〕,andcontrolstructure〔interactionamongtheblocks〕.参考图,我们看到信号处理技术是预处理所需要的,模式识别技术是分割、特征提取以及分类所需要的,而人工智能技术那么是结构分析、知识获取及表示〔世界模型〕以及限制结构〔块间交互〕所需要的.Thepictureelementsacrossalineareconvertedtothevideosignalandlow-passfilteredwithanelectricalfilter.Thissmoothingremovesthediscretestructureinthehorizontaldimension.沿着一条直线的图像像素被转换成视频信号,然后由一个电子滤波器进行低通滤波.这一平滑处理可消除水平方向的离散结构.Unit13ExercisesTranslatethefollowingsentencesintoChinese.Theprecedingchaptershavedescribedhowtheautomaticcomputerperforms,buthavenotdescribedhowtheautomaticcomputercanbeputtousetododatahandlingworktoserveanorganization,norwhysuchworkisdoneinthewaythatitis.前面的章节讲述了自动计算机是如何工作的,但没有讲述自动计算机如何能用于数据处理工作以效劳于一个机构,也没有讲述这种工作为什么用这种方法实现.Whilethesubjectofcodingoftencarrieswithitanairofsecrecy,amoreimportantmotiveinmanycodingsystemsistheimprovedefficiencyinconveyinginformation.如果说编码这一主题常带有一种秘密的色彩,那么许多编码系统的一个更重要的目的那么是为了提升信息传递的效率.Unit14Exercises(1)TranslatethefollowingsentencesintoChinese.1.Theimportanceofearlybraindevelopmentinsettingthefoundationsforlanguageisapparentinbabiesyoungerthan6months.大脑的早期开展对于奠定语言根底的重要性在六个月以下的婴儿中是显而易见的.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.数字图数字图像处理包括了多种多样的技术和数学工具,每一项应用都涉及到一系列的处理步骤.这些步骤是以大量不同次序排列的各种模块,每一模块通常容许一些参数值的技术指标,从而进一步扩大了为获得预期结果而可能采取的处理方案的选择范围.与模拟图像(即胶片)相比,数字图像的主要优点在于数据的质量和数据可供计算机进行处理这两方面.质量方面的优越性实际上是以下两种优越性的综合：动态范围：数字图像可表现128级或更多的灰度,而胶片产品只能分辨15至30级；重现性：一幅数字图像屡次复制后仍与原件包含完全相同的信息,而一幅第四代的照片与原件相比却大大地退化(损伤)了.Unit16ExercisesTranslatethefollowingsentencesintoChinese.Inrecentyears,therehasbeenatremendousincreaseintheuseofdigitalcomputersandspecial-purposedigitalcircuitryforperformingvariedsignalprocessingfunctionsthatwereoriginallyachievedwithanalogequipment.近年来为实现各种信号处理功能,数字计算机和专用数字电路的使用有了巨大的增长,这些处理功能原先都是用模拟设备实现的.Inthebeginning,computerswereusedtoprocessonlynumericalinformation,butmajorityofourinformationisnon-numericalinnatureandverylittleisknownaboutitsdescriptionandprocessing.一开始计算机只是被用来处理数值信息,而我们的大多数信息都是非数值性质的,而且人们对这些信息的描述和处理所知甚少.Unit17ExercisesTranslatethefollowingpassagesintoChinese.Forthefirsttimeeverthelandscapeischanging,ashighvolumepersonalcomputermultimediaapplicationsproliferate.Firstaffectedweremonitors,whichfor

sosometimehaveofferedhigher-than-broadcastspeedandresolution.Onecanexpectcamerastofollow,withhigh-speed,high-resolutiondevicesdrivenbyconsumerdigitalstillcameratechnologyandlower-resolution,ultralowcostunitsdrivenbyentertainment,internetconferencing,andperceptualuserinterfaceapplications.随着大量个人计算机多媒体应用的急剧增加,情况首次发生了变化.最早受到影响的是显示器,相当长时间以来它已经能够提供比播送级更高的分辨率和速度.人们可期待照相机/摄像机也随之跟上,包括由民用数字照相机所推动的高速度、高分辨率器件,娱乐业、互联网远程会议和用户视觉界面应用所推动的低分辨率和极低价格的设备.IfyoualreadyhavethefastestCPUinaparticularfamilyandstillwantmoreperformance,thenitmaybemorecost-effectivetoaddsystemRAMorcacheRAMthantoputinaprocessorfromadifferentfamily.Addingsystemmemorycanbringsignificantperformanceincreasesatarelativelylowcost,assumingyouconfigurethememorycorrectly.InadditiontoaddedcacheandsystemRAM,afasterandlargerharddrivecansaveyoutimewhenrunningapplicationsdependentonheavydriveaccessanddatathroughput.Addingagraphicsacceleratorcardcanhelp,too,especiallyifyouarelookingforawaytostayawakewhileyoursystemredrawsimages.如果你已经有了某一系列中最快的CPU而还想要更多的性能,那么增加系统RAM或高速缓存RAM也许比插入一枚另一系列的处理器更合算.特别是如果彳是一名Windows用户,假设你正确地配置内存,那么增加系统内存可以较低的代价带来可观的性能提升.除了增加高速缓存或系统RAM,一个更快和更大的硬盘可在运行依赖于大量读写硬盘和有大量数据吞吐时节省你的时间.增加一个图形加速器也是有益的,如果你使用Windows,而且发现你在寻找某种途径使你在系统重显图象时能保持“清醒〞,那么尤其是如此.

3.Inuniversityenvironments,MATLABhasbecomethestandardinstructionaltoo3.forintroductorycoursesinappliedlinearalgebra,aswellasadvancedcoursesinotherareas.Inindustrialsettings,MATLABisusedforresearchandtosolvepracticalengineeringandmathematicalproblems.Typicalusesincludegeneralpurposenumericalcomputation,algorithmprototyping,andspecialpurposeproblemsolvingwithmatrixformulationsthatariseindisciplinessuchasautomaticcontroltheory,statistics,anddigitalsignalprocessing(time-seriesanalysis).在大学环境里,它已成为应用线性代数导论以及其他领域中许多高级课程的标准教学工具.在工业界,MATLAB被用于研究和解决实际的工程和数学问题.典型的应用包括通用数值计算、算法原型测试以及使用矩阵公式的专门问题的解决,这些问题是在自动限制理论、统计、数字信号处理(时间序列分析)等学科中提出来的.Multimediaisagenerictermformultimediacomputing“orinteractivemultimedia〞.Thecomputerandsoftwareareusedtocontrolandnavigatethroughthecommunicationslinks,notonlyoneatthetime,butseveralsimultaneously.Computersystemshavebeenmostdevelopedinusingvisionandhearingtointerfacebetweenthedigitalandanalogueworlds,e.g.,stillandmovingimages,textandgraphicsusethevisualsenses,andaudiouseshearing.Multimediaisdefinedasvisual,audioandtextualinformationwhichcanbepresented,separatelyorsimultaneously,toconveyandpresentinformationinteractivelytousers.Itistechnicallyeasytodigitizetheanalogueformsofthesecommonmediaandhandledbycomputersnowwidelyavailableandinexpensivetobeaccessibletomostusers.多媒体是表示“多媒体计算〞或“交互式多媒体〞的一般术语.计算机和软件被用于限制并通过不止

一条通信链接同时进行浏览.在利用视觉和听觉在数字和模拟世界之间进行交互方面,计算机系统已得到极大的开展,例如对静止和活动图像、文本和图形使用视觉,对音频使用听觉.多媒体被定义为可以分别或同时展现的视频、音频、文本信息,用以交互式地将信息传递和展示给用户.技术上很容易将这些普通媒体的模拟形式用计算机实现数字化并加以处理,计算机现在已十分普遍,其价格廉价,大多数用户都能使用.Theessentialcapabilityofanymultimediacomputersystemistheabilitytoconverttheanaloguesignaltoadigitalformatandtocompressthisinformationusingstandardalgorithms.ThepoweroftheCPUwilldeterminewhetherthisprocesscanbecarriedoutinreal-timeorwhetherithastobedoneoff-line.OriginallythispoweronlyexistedinUNIXsystems,butmorerecentlyithasbecomeavailableinPCsandMacintosh.Thecompressionprocessisnecessaryotherwisethequantityofdatatobestoredandtransmittedwouldbeexcessive.MostPCshaveuntilrecentlydependeduponhardwareencoding/decodingsystems,butthespeedofcurrentprocessorsissuchthatsoftwarecompressionsystemshavebeendeveloped.Theadvantageofthesoftwaresystemsisthatthecompatibilityandinteroperabilityissuescanbehandledmoreeasily,andthecostoftheequipmentisnotraisedbytheneedtopurchaseexpensivehardwaredevices.任何多媒体计算机的根本功能是将模拟信号转换成数字格式,并用标准算法将此信息压缩的水平.CPU处理水平将决定是否能实时完成此过程还是必须离线执行.原先只有UNIX系统才有这种实时而且不会因购置水平,但近年来PC和Macintosh也能胜任〔有这种水平〕了.压缩是必须的,否那么要存储和传送的数据量太大.直到不久前大多数PC还依赖硬件编解码系统,而目前的处理器速度已使软件编解码系统的开发成为可能.软件系统的优点在于可更方便地处理兼容性和协而且不会因购置昂贵的硬件而提升设备本钱.Unit19ExercisesTranslatethefollowingparagraphsintoChinese.ArtificialIntelligenceisabranchofsciencethathelpsmachinesfindsolutionstocomplexproblemsinahuman-likefashion.Thisgenerallyinvolvesborrowingcharacteristicsfromhumanintelligence,andapplyingthemasalgorithmsinacomputerfriendlyway.Computersarefundamentallywellsuitedtoperformingmechanicalcomputationsusingfixedrules.Thisallowsmachinestoperformsimplemonotonoustasksefficientlyandreliably,whichhumansarenotsuitedto.Unlikehumans,however,computershavetroubleinunderstandingspecificsituations,andadaptingtonewsituations.ArtificialIntelligenceaimstoimprovemachinebehaviorintacklingsuchcomplextasks.Humanshaveaninterestingapproachtoproblem-solving,basedonabstractthought,high-levelreasoningandpatternrecognition.ArtificialIntelligencecanhelpusunderstandthisprocessbyrecreatingit,thenpotentiallyenablingustoenhanceitbeyondourcurrentcapabilities.人工智能是一个科学分支,它可以帮助机器找到像人那样解决复杂问题的解.这通常包括从人的智能中借用一些特征,应用这些特征开发出便于计算机实现的算法.计算机原那么上适合于根据固定的编程规那么进行机械性的计算,这使得机器能够有效而可靠地执行简单单调的任务,这正是人所不擅长的.然而不同于人,计算机难以理解特定的情形,适应的新情况.人工智能的目标就是改良机器的性能以对付这种复杂的任务.人类具有一种解决问题的有趣水平,这种水平是基于抽象思维、高级推理和模式识别的.人工智能可以通过重建这一过程来帮助我们理解它,进而使我们的水平有可能超越当前的水平.Itisrarethattheoptimizationwill