信息科学与电子工程专业英语课后答案

第页Unit1Exercises(1)TranslatethefollowingsentencesintoChinese.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及重量都及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，或者在供应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。留意，在本书中粒子运动仅限于金属的状况不属于电子学。Hardwaretechnologieshaveplayedvitalrolesinourabilitytouseelectronicpropertiestoprocessinformation,butsoftwareanddataprocessingaspectshavenotdevelopedatthesamespeed.硬件技术在我们运用电子特性来处理信息的实力中始终起着重要作用，而软件及数字处理方面却没能及硬件同步发展。However,inaproperlydesignedDCamplifiertheeffectoftransistorparametervariation,otherthanIco,maybepracticallyeliminatediftheoperationpointofeachstageisadjustedsothatitremainsinthelinearoperationrangeofthetransistorastemperaturevaries.然而在设计得当的直流放大器中，若调整每一级的工作点使之在温度变化时保持在晶体管线性区，就能在事实上消退Ico以外的晶体管参数变化所造成的影响。Unit2Exercises(1)TranslatethefollowingsentencesintoChinese.Ifanalogsignalsaretobetransmitteddigitally,theyfirsthavetobesampledataspecifiedrateandfurtherconvertedtodiscreteamplitudesamplesbyquantization.假如要以数字方式传输模拟信号，首先必需以肯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基础。Stabilityandrepeatabilityarefundamentalattributesofdigitalcircuits,however,andthenecessaryaccuracycanbeobtainedinadigitalversionofthemodulatorbyanappropriatechoiceofwordlengthtorepresentthesignals.不过稳定性和可重复性是数字电路的基本性质，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基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。Unit3Exercises(1)TranslatethefollowingsentencesintoChinese.Averycommonlyusedmethodofmicrowavemeasurementsisbasedonthestudyofastandingwavepatternformedalongthelinebecauseoftheinterferenceofincidentandreflectedwaves.一个很常用的微波测量方法是基于对驻波图型的探讨，这种驻波是由入射波和反射波之间的干涉而沿着传输线形成的。Computationsshowareductionof6dBintheEMfieldintensitywiththedistancedoubled,andanincreaseof3dBintheintensitywiththetransmittedpowerdoubled.Thisresultprovidesverificationtothealgorithmused.计算表明，当距离增大一倍时，电磁场强度减小6分贝；而放射功率增大一倍时，场强则增加3分贝。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.在电路设计中运用CAD的其它动机包括：想要验证用别的方法设计出来的电路；满足新奇心或者可能是想发觉预想不到的现象。后一个动机并非是最不重要的。（取得信念，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，以便这些放大器供应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心的，将来的政治活动将基于信息时代的事物，面对信息的存储,爱护和交换。Unit4Exercises(1)TranslatethefollowingpassagesintoChinese.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须要有一个通信系统。在通信系统内部，信息的传输常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复原出来。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困难的技术。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.电子通信就是通过运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：支持信息流淌所须要的设备，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，安排,实施,操作通信系统的人员，以及对全部这些资源的管理。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,andsecurityproblemsduetothesimpleradiointerfaceused.Secondgenerationsystemswereintroducedintheearly1990’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，而且因为运用简单的无线电接口而存在安全问题。第二代通信系统于20世纪90年代初开始引入，全部运用数字技术。通过在传输前将话音波形压缩使得用户容量提高了三倍。第三代通信系统是对第二代系统在困难性方面的扩展，预料于2000年以后启用。通过运用困难的复用技术如CDMA或TDMA的扩展，并提高服务的敏捷性使得系统容量比原来的第一代系统提高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），并以简单求值的形式表示。全部考虑的相应于实际信道的状况，以及很多状况下得到的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，依据消息信号的函数有规则的变化。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。本书相当大部分内容是探讨如何设计调制方案以实现上述任务。一个通信系统的胜利很大程度上依靠于调制。Unit5Exercises(1)TranslatethefollowingpassageintoChinese.OFDMconsistsofalargenumberofsubcarriersequallyspacedinafrequencyband,eachmaybedigitallymodulatedbyasameschemesuchasPSK,QAM,etc.,orbydifferentschemes.Aseriallytransmittedsequenceisdividedintoanumberofsections,eachhavingNsymbols,andtheNsymbolsineachsectionareusedtomodulateNcarriersforsimultaneoustransmission.ThereforeOFDMisessentiallyaparallelmodulationsystem.Whenthenumberofsubcarriersissufficientlylarge,thesystemcanresistmultipathinterference.Thisisbecausethat,inthetimedomain,asymboldurationlongerthanthemultipathdelaycanbechosen,whileinthefrequencydomain,eachsymbolonlyoccupiesasmallportionofthechannel’sfrequencyband.Thus,theeffectofmultipathfadingspreadsovermanysymbols,resultinginslightdistortiontomanysymbolsratherthancompletedestroyofafewsymbols.Inthisway,correctdemodulationisnotaffectedsothatthesignalcanbeaccuratelyrecoveredatthereceiver.InanOFDMsystem,theprincipleofchoosingthesubcarrierintervalistomakethesubcarriersmutuallyorthogonalwithintheentiresymbolperiod.Thus,evenifspectraloverlapexistsbetweenthesubcarriers,thesymbolscanstillberecoveredwithoutloss.Inordertorealizemaximumspectralefficiency,theintervalbetweensubcarriersisusuallychosentoequalthereciprocalofthesymboldurationT.Thereforethesubcarrierfrequenciesinthebasebandarefn=n/T,(n=0,1,...,N1).Denotingthen-thmodulatingsymbolasX(n),theOFDMwaveformwithinasymboldurationcanbeexpressedas: (1)Samplingthiswaveformatt=T/Nyields (2)Itisobservedfromtheaboveexpressionthatx(k)andX(n)formadiscreteFouriertransformpair,thereforethebasebandOFDMwaveformcanbegeneratedfromthediscreteFouriertransformofNmodulatingsymbols.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很多段，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实力。这是因为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部分，因此多径衰落的影响被分散到很多符号上，其结果是很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，信号能在接收器中精确地复原。在OFDM系统中，选择子载波间隔的原则是使子载波在整个符号周期内相互正交，这样。即使在子载波间存在频谱部分重叠，符号仍能无损失地复原。为了实现最大的频谱效率，子载波之间的间隔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)，在一个符号周期内的OFDM波形可表示： (1)在t=T/N时刻采样这个波形得到： (2)从上面的表示中可以看到，x(k)和X(n)构成了一对离散傅里叶变换，因此基带OFDM波形可依据N个调制符号的离散傅里叶变换来生成。当N=2m，其中m为整数，IDFT的快速算法很简单实现。Unit6Exercises(1)TranslatethefollowingsentencesintoChinese.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料。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。至今依旧如此。然而电信及计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.在一本书中供应如此大量的系统性能曲线，使探讨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较探讨，从而在他或她所面临的限制之下做出最佳的选择。Thechannelprovidestheelectricalconnectionbetweentheinformationsourceandtheuser.Thechannelcanhavemanydifferentformssuchasamicrowaveradiolinkoverfreespace,apairofwires,oranopticalfiber.信道供应信息源和用户之间的电路联接。信道可以有很多不同的形式，比如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志向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基本问题。Unit8Exercises(1)TranslatethefollowingsentencesintoChinese.Earlyinthetwentiethcentury,itwasfoundthatlightcouldcauseatomstoemitelectronsandthat,whenlightreleasedanelectronfromanatom,theenergypossessedbytheelectronverygreatlyexceededthatwhichtheatomcould,accordingtotheelectromagneticwavetheory,havereceived.在二十世纪早期，人们发觉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.脉冲的展宽确定了相邻脉冲之间的最小间隔，这一间隔进而又确定了光纤的最大信息容量。Ifoneweretotransmitsuchinformationwithoutimpressingitonanopticalcarrierbutinsteadonaradiofrequency(RF)carrierabithigherthanthemaximumrate,thetransmissionwavelengthoftheRFcarrierwouldbecentimetersorlarger.假如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，则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.光波波长之小使放射和接收模块得以小型化，这就使光通信系统的尺寸,重量以至价格及相应的微波,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全部优点还有待于落实在详细成果中，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，可以运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很多领域具有竞争力的小巧的宽带系统，这些领域中特殊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）成本并非电信系统中真正重要的考虑因素，通信设备的成本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，集总单元则成为电磁谐振器。UNIT101.Theprincipleswhichunderliealmostalldigitalaudioapplicationsanddevices,betheydigitalsynthesis,sampling,digitalrecordingorCDoriPodplayback,arebasedonthebasicconceptswhichfollowinthischapter.Newformsofplayback,,compressionandstorageofdataareallchangingonaseeminglydailybasis,buttheunderlyingmechanismsforconvertingreal-worldsoundintodigitalvalues,manipulatingthosedataandfinallyconvertingthembackintoreal-worldsoundhasnotvariedmuchsinceMaxMathewsdevelopedMUSICIin1957atBellLabs.全部的数字音频应用程序和设备是在数字合成,采样,数字录音或CD或iPod播放的基础上，都是基于最基本的概念,遵循在这一章的原则。新形式的播放,文件格式,压缩和存储的数据都在一个看似每天改变，但是这种联系的潜在机制转换为现实世界的声音转化为数字值,操纵这些数据,最终将他们转化成真实世界的声音没有变化多少，因为马克斯·马修斯在贝尔试验室于开发了音乐于20世纪60年代。2.Soundiscreatedbyvibrations,suchasthoseproducedbyaguitarstring,vocalcordsoraspeakercone.Thesevibrationsmovetheairmoleculesnearthem,forcingmoleculestogether,asaresultraisingtheairpressureslightly.Theairmoleculesthatareunderpressurethenpushonairmoleculessurroundingthem,whichpushonthenextsetofairmolecules,andsoforth,causingawaveofhighpressuretomovethroughtheair;ashighpressurewavesmovethroughtheair,theyleavelowpressureareasbehindthem.Whenthesepressurelowsandhighs–orwaves–reachus,theyvibratethereceptorsinourears,andwehearthevibrationsassound.声音是由振动产生的,如制作的吉他弦,声带或扬声器锥。这些振动移动旁边的空气分子，使分子连接在一起，因此提高空气压力略。这是在压力下将空气分子四周的空气分子，从而推动下一组空气分子等等,导致一波高压进入空气;高压力波通过空气移动,他们身后留下低压区域。当这些压力低点和高点——或波动——到达我们,他们在我们的耳朵振动接收,我们听到时发出的振动声。3.Unlikeanalogstoragemediasuchasmagnetictapeandvinylrecords,computersstoreaudioinformationdigitallyasaseriesofzerosandones.Indigitalstorage,theoriginalwaveformisbrokenupintoindividualsamples.Thisisknowasdigitizingorsamplingtheaudio,andissometimescalledanalog-to-digitalconversion.Thesamplingratedefineshowoftenasampleistaken.Forexample,CD-qualitysoundhas44.100samplesforeachsecondofawaveform.不像模拟存储媒体如磁带和唱片,计算机存储音频信息数字化是一系列由0和1组成。在数字存储,原始波形分解成单独的采样。众所周知作为数字化或抽样音频,有时被称为模拟数字转换。采样率定义频率取样时。例如,cd品质的声音有每秒钟44.100采样波形。4.Thehigherthesamplingrate,theclosertheshapeofthedigitalwaveformwillbetotheoriginalanalogwaveform.Lowsamplingrateslimittherangeoffrequenciesthatcanberecorded,whichcanresultinarecordingthatpoorlyrepresentstheoriginalsound.采样率越高，数字波形的形态越接近原来的模拟波形。低采样率限制频率的记录范围，从而导致记录不充分，难以表示原始的声音。5.Thesamplingratelimitthefrequencyrangeoftheaudiofile;toreproduceagivenfrequency,thesamplingratemustbeatleasttwicethatfrequency.Forexample,iftheaudiocontainsaudiblefrequenciesashighas8,000Hz,yourneedasamplerateof16,000samplespersecondtoreproducethisaudioaccuratelyindigitalform.ThiscalculationcomesfromtheNyquistTheorem,andthehighestfrequencythatcanbereproducedbyagivensamplerateisknownastheNyquistFrequency.CDshaveasamplingrateof44,100samplespersecondthatallowssamplesupto22,050Hz,whichishigherthanthelimitofhumanhearing,20,000Hz.采样率限制的音频文件的频率范围从而复制一个给定的频率，采样率必需至少两倍的采样频率。例如,假如音频包含声音频率高达8000赫兹,你须要一个采样率为每秒16000个样本复制本音频精确数字形式。这个计算来自于奈奎斯特定理,和最高的频率可以复制出一个给定的采样率是众所周知的奈奎斯特频率。cd有一个采样率的每秒44100个样本,允许样本22050赫兹,这是高于人类听觉的极限,20000赫兹。Uint111.Theyaretransmittinghigh-resolutionfullcolorimagesattherateof30imagespersecond,atransferspeedthatenablesfullsizefullqualityimageviewinginrealtime.他们在以30帧每秒的速率传输高辨别率全彩色图像，传输速度能使全尺寸的完整的图像质量实时查看。2.Animageisa2-dimensionaldistributionofenergy,typicallyofvisibleelectromagneticradiation(light)butcanalsobeofx-rays,ultraviolet,infraredorotherradiation:electrons,acousticwavesorevennuclearparticles.图像是一个能量的二维分布，通常是可见的电磁辐射（光）也可以是X射线，紫外线，红外线或其它辐射：电子，声波甚至核粒子。3.Highresolutionandfullcolorareimportantforsuchexaminationsofstandardpreparedspecimens,butresolutionandcolorsmaybereducedforfreezesectionserviceasthesespecimensarelowindetailsandgrowthpatternistheprevailingfeatureanalyzed.高辨别率,全彩色是重要的对于这样的考试标准制备试样,但辨别率和颜色可降低标准冷冻切片服务，这些标本是低的细微环节，增长模式是被分析过的流行特征。4.Imagediscontinuities,ontheotherhand,usuallycorresponddirectlytoobjectsurfacediscontinuities(e.g.,edges),sincetheotherfactorstendnottobediscontinuous.Imagediscontinuitiesaregenerallyconsistentgeometrically(i.e.,inshape)evenwhennotconsistentphotometrically.图像的不连续性，另一方面，通常直接对应于物体表面的不连续性（例如，边缘），由于其他因素往往不间断。图像的不连续性通常包括是几何图形（即，几何形）即使不一样的光度测定。5.Inatelevisionscanninggeneratorusingapairoffree-runningrelaxationoscillators,free-runningfrequenciesoftheoscillatorsaresetslightlybelowthehorizontalandverticalpulserates,andthestrippedpulsesareusedtotriggertheoscillatorsprematurelyandthustosynchronizethemtothelineandhalf-framerates.在采纳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，分别出来的脉冲被用来提前触发振荡器从而使它们及行频和半帧频（场频）同步。6.Theneedforindividualtreatmentofimagesmakesstrongdemandsonthemethodology,butthefactthatdifferentfeaturesareimportantindifferentapplicationsalsoopensnewpossibilitiesregardingdatareduction.用于图像处理的须要使得个体方法论的剧烈需求，但事实上，不同的功能在不同的应用程序也很重要，对于减少数据打开新的可能性。UNIT121.Althoughsomenativespeakershaveproblemsinpronouncingsomesoundstheyareperceivedasnativespeakersbasedontheirprosodyandvocabulary.尽管一些母语在发音上有问题，一些基于他们的韵律和词汇的语言被视为母语。2.Amoreadaptabletechniqueisedgefinding,whichdetectstheregionsofhighrateofchangeoftoneinanimage,onthebasisthatthesearelikelytoindicateedgesofobjectsorROI.检测高清图像中的色调变化率最适合的技术是边缘检测，基于此，这些可能表明物体或区域的边缘。3.Manyoftheseearlysystemshadadvantagesthatseemedexcitingandintuitivewhendemonstratedwith“toy”programs,butranintodifficultproblemswhenattemptsweremadetoextendthemtomorerealistically-sizedprograms.这些早期的系统优势，好像令人兴奋的和直观的表现及“玩具”的项目，但遇到困难的问题时，曾试图扩大他们更多的实际程序的大小。。4.Referringtothefigure,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须要的，模式识别技术是分割,特征提取以及分类所须要的，而人工智能技术则是结构分析,知识获得及表示（世界模型）以及限制结构（块间交互）所须要的。5.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。这一平滑处理可消退水平方向的离散结构。6.Theseproductsusecommerciallyavailablespeechtoolkits,suchastheIBM’sViaVoice,Dragon’sNaturallySpeaking,orL&H’sVoiceXpress,whichwerecreatedforbuildingvoice-enabledapplicationsfornativespeakersratherthanforteachingforeigners.这些产品运用市售的语音工具包，如IBM的一款声控软件，现代月刊的自然演讲，或L&H的威狗论坛动漫嬉戏杂志，分别建立语音创建启用的应用程序，这款程序为学习母语的人而不是为了教外国人。7.Thethreemajorformsofelectronicdocumentsmentionedabovehaveasignificantimpactonthewaysinwhichusersselecttomanagethedocuments’lifecyclecomprisingcreationorreceptionfromanoutsideentity,processing,storage,retrievalandpublishing.电子文件上面提到的三种主要形式有关于如何在用户选择的文件管理，文件管理的生命周期包括产生或接收从外部实体，处理，存储，检索和发布。8.Unfortunatelyinmostapplicationssceneshadingissuchthatobjectscannotbeseparatedfrombackgroundbyanythreshold,andevenwhenanappropriatethresholdvalueexistsinprincipleitisnotoriouslydifficulttofinditautomatically.不幸的是，在大多数应用中场景阴影的物体不能被任何阈值从背景分别，甚至当一个合适的阈值原则存在但是难以自动找到它。UNIT131.Asolidnetworkdesigniscrucialformaintainingasecurenetwork.Fromperimeterfirewallstolockingdownendpointdevicesandcontrollinguseraccess,theseresourceshelpyoubuildasecurelayerednetworkandidentifyvulnerabilitiestopreventattacks.一个坚实的网络设计是维护网络安全的关键。从防火墙来锁定终端设备和用户访问限制，这些资源帮忙你建立一个安全的分层网络，找出漏洞以防止攻击。2.Intrusionmanagementismorethanatooloraperson—itisalsoaprocess.Theseresourcesarmyouwiththeknowledgeyouneedtoimplementandmaintainanintrusionmanagementlifecycle.入侵管理不仅仅是一种工具或一个人，它也是一个过程。这些资源为您供应你须要实现和维护一个入侵管理生命周期。3.Severalclassesofhumanerrorhavebeenidentifiedandstudied,andconditionsthatincreasethelikelihoodoferrorcanbespecifiedinadvance.几类人类的错误已经被识别和探讨和条件,增加错误的可能性可以事先指定。4.Similarattemptsinotherindustrieshavefailedbecausetheirreportsweresubmittedthroughachainofauthoritythatincludedtheperson’ssupervisororplantmanagement(peoplewhohavebiasestosanitizethereportortoformnegativejudgmentsofthereporter.在其他行业类似的尝试都失败了因为他们的报告是通过一连串的权威，包括职员的主管或公司管理(一些对报告有偏见或形成的不良报道的记者。5.Theprecedingchaptershavedescribedhowtheautomaticcomputerperforms,buthavenotdescribedhowtheautomaticcomputercanbeputtousetododatahandlingworktoserveanorganization,norwhysuchworkisdoneinthewaythatitis.前面的章节讲解并描述了自动计算机是如何工作的，但没有讲解并描述自动计算机如何能用于数据处理工作以服务于一个机构，也没有讲解并描述这种工作为什么用这种方法实现。6.Thesourcesoftheinformationareoftenreportsinthemedia,reportsthatareincomplete,usuallywrittenbeforeallrelevantinformationisgathered,andsubjecttoothersourcesofinaccuraciesandbiases.这些资料的来源通常是媒体报道,由于报告不完整,通常在写之前进行相关信息收集,并受其他来源的错误和偏见。7.Thethreatisalsoplacedinatheoreticalpoliticalcontextbyexamininghowitrelatestoparadigm-shiftingtechnologiesofthepast,whatitsattractionsanddeterrentsare,andhowitwouldbeanalyzedandaddressedwithintraditionalrealist/liberalnationalsecurityschools.威胁也看它涉及范式转换的过去的技术放在一个理论的政治背景下，它的吸引力和威胁是什么，以及它将如何分析和在传统的现实主义/自由国家安全学校解决。8.Whilethesubjectofcodingoftencarrieswithitanairofsecrecy,amoreimportantmotiveinmanycodingsystemsistheimprovedefficiencyinconveyinginformation.假如说编码这一主题常带有一种隐私的色调，那么很多编码系统的一个更重要的目的则是为了提高信息传递的效率。UNIT141.Telemedicinehasproventobeeffectiveasadisasterresponse,ameaningfulaidforthethirdworld,carefortheelderlyandchronicallyillintheirhomes,aswellasaproviderofhealthcaretoremoteorisolatedareas.远程医疗系统已经被证明是个灾难响应有效的作为之一，一个有意义的救济第三世界,照看老年人和慢性病患者在他们的家园,以及医疗保健供应商远程或偏远地区。2.Thecontinuedsurgicalprocedureisincertaincasesdependentonthistypeofpathologyservice,andhospitalswithoutac