简介:Theequationoftime-domainwavepropagationindispersivemediaandtheexplicitbeampropagationmethodarepresentedinthispaper.Thismethodisdemonstratedbytheshortopticalpulsesinadirectionalcouplerwithsecondorderdispersiveeffectandshowstobeinfullagreementwithformerreferences.Thismethodissimple,easyandpractical.
简介:Theterahertztime-domainspectroscopy(THz-TDS)systemandtherelatedtechnologyandtheapplicationsinCapitalNormalUniversityarepresented.ThemostoftenusedTHz-TDSsystemasaspectroscopicmeasurementsetupinourlabisintroducedindetail,includingtheTHzradiationsource,theTHzdetectionmethodanditsmeasurement,andthecontrolsystem.THzspectraofvariousmaterialsissummarizedanddiscussed.Thesematerialsincludebutnotlimitedtotwokindsoftypicalmatter—theillegaldrugsandexplosives.Thebiologicalmacro-molecules,cosmeticsandfinechemicalmaterials,ediblepigmentsandfoodadditives,homocysteicacidandrelatedcompounds,heavyionsinsoil,Chinesemedicines,tobaccoandcrops,oilandchemicalproducts,carbonnanotubes,superconductors,andvarioussemiconductorsandtheirheterojunctions,arepresented.THzemissionsfromtheInAsandInNsemiconductorssurfacearecompared.THzspectralinvestigationofmetallicmeshstructuresissummarized.Finally,anoutlookofTHzspectroscopicapplicationsisgiven.
简介:Time-domainWavePropagationinDispersiveMedia①JUZhenle,FUJunmei,FENGEnxin(InstituteofMicrowaveEnginering&OpticalCommunicationTe...
简介:在时间域的领域分解和匹配的方法为模仿在波浪进展的轮船的运动被构画出。流动域被想象的控制表面分解成内部、外部的域,并且当短暂格林函数方法在外部域被使用时,Rankine来源方法被用于内部域。二个起始的边界价值问题在控制表面上被匹配。相应数字代码被开发,并且为系列60轮船和S175货柜船在头海进展的增加的群众,波浪激动力量和轮船运动,被介绍并且验证。当数字结果与试验性的数据和另外的引用相比时,一个好协议被获得了。它证明因为面板discretization,现在的方法在数字计算期间在内部领域仅仅是更有效的,并且好数字稳定性被证明与闪光关于轮船避免分叉问题。
简介:Directtime-domainsimulationoffloatingstructureshasadvantages:itcancalculatewavepressurefieldsandforcesdirectly;anditisusefulforcoupledanalysisoffloatingstructureswithamooringsystem.Atime-domainboundaryintegralequationmethodispresentedtosimulatethree-dimensionalwaterwaveradiationproblems.Astableformoftheintegrationfree-surfaceboundarycondition(IFBC)isusedtoupdatevelocitypotentialsonthefreesurface.Amulti-transmittingformula(MTF)methodwithanartificialspeedisintroducedtotheartificialradiationboundary(ARB).Themethodwasappliedtosimulateasemi-sphericalliquefiednaturalgas(LNG)carrierandasemi-submersibleundergoingspecifiedharmonicmotion.NumericalparameterssuchastheformoftheARB,andthetimeandspacediscretizationrelatedtothismethodarediscussed.Itwasfoundthatagoodagreementcanbeobtainedwhenartificialspeedisbetween0.6and1.6timesthephasevelocityofwaterwavesintheMTFmethod.Asimulationcanbedoneforalongperiodoftimebythismethodwithoutproblemsofinstability,andthemethodisalsoaccurateandcomputationallyefficient.
简介:Thetime-domainElectroMagnetic(EM)scatteringbyburiedobjectsindispersivemediaiscalculatedwithFD-TDmethod.TheFD-TDformulainDebyedispersivemedia(boththecomplexpermeabilityandthecomplexpermittivityaredescribedbyDebyeequations)arededuced,andtheabsorbingboundaryconditionisgiven.ThevalidityofFD-TDmethodinlossymediaisverifiedthroughcomparingtheFD-TD’sresultsandtheotherones.Thepropagationoftransientpulsesindispersivemediaisstudiedindetail.Thescatteringpulsesandthewiggletracesfortypicalburiedobjectsaregiven.
简介:Nonlinearwaveloadscaninducelow-frequencyandhigh-frequencyresonancemotionsofamooredplatformindeepwater.Fortheanalysisofthenonlinearresponseofanoffshoreplatformundertheactionofirregularwaves,themostwidelyusedmethodinpracticeistheCumminsmethod,inwhichthesecond-orderexcitingforcesinthetimedomainarecomputedbyatwo-termVolterraseriesmodelbasedonincidentwaves,first-orderbodymotionresponse,andquadratictransferfunctions(QTFs).QTFsarebichromaticwavesactingonabodyandarecomputedinthefrequencydomaininadvance.Formovingbodies,QTFsarerelatedtothefirst-orderbodyresponse,whichistobedeterminedinthesimulationprocessofbodymotionresponsebutisunknowninthecomputationprocedureofQTFs.Insolvingthisproblem,TengandCong(2017)proposedamethodtodividetheQTFsintodifferentcomponents,whichareunrelatedtothebodyresponse.WiththeapplicationofthenewQTFcomponents,amodifiedCumminsmethodcanbedevelopedforthesimulationofthenonlinearresponseofamooredfloatingplatform.Thispaperpresentsareviewofthetheory.
简介:ThispaperdescribesaLeastSquares(LS)channelestimationschemeforMIMOOFDMsystemsbasedontime-domaintrainingsequence.Wefirstcomputetheminimummeansquareerror(MSE)oftheLSchannelestimation,andthenderivetheoptimalcriteriaofthetrainingsequencewithrespecttotheminimumMSE.Itisshownthatoptimaltime-domaintrainingsequenceshouldsatisfytwocriteria.First,theautocorrelationofthesequencetransmittedfromthesameantennaisanimpulsefunctioninaregionlongerthanthechannelmaximumdelay.Second,thecross-correlationbetweensequencestransmittedfromdifferentantennasiszerointhisregion.Simulationresultsshowthattheestimatorusingoptimaltime-domaintrainingsequenceshasbetterperformancethanthatusingoptimalfrequencytrainingsequenceatlowsignal-to-noiseratio(SNR).Toreducethetrainingoverhead,asuboptimaltrainingsequenceisalsoproposed.Comparingwithoptimaltrainingsequence,ithaslowcomputationcomplexityandhightransmissionefficiencyattheexpenseoflittleperformancedegradation.
简介:Inthiswork,wereviewthedevelopingprogressoftwo-dimensionalterahertztime-domainspectroscopy(THz-TDS)anditsdiverseapplications,includinganalyzingthepolarizationofTHzradiationfromalaser-inducedplasmasourceandstudyingthecorrespondingphysicalmechanism,andcharacterizingtheopticalpropertiesofcrystals,etc.
简介:Time-domainanalysisisusedtopredictwaveloadingandmotionresponsesforashiptravellingataconstantspeedinregularobliquewaves.Thecombineddiffractionandradiationperturbations,causedbythesteadyforwardspeedoftheshipandhermotions,areconsideredasadistributionofnormalvelocitiesonthewettedhullsurface.Theship-hullboundaryconditionisexactlyfulfilledbyexpressingthefluidnormalvelocitiesasafiniteseriesintermsofthebodygeometryandtheincidentwavepotential.Asfarastheauthorsareaware,nosimilarworkispublishedtodate.ThenewtheoryisappliedtopredictforcesandmotionsatforwardspeedforaWigleyship-hullinheadwavesandacatamaran-ferryinobliquewaves.PredictionsarecomparedwithpublishedtheoreticalandexperimentalresultsfortheWigleyship-hull,andthecomparisonisgood.Forthecatamaran,aself-propelledmodelisbuiltandtestedinthelargetowingtankandseakeepingbasinoftheChinaShipScientificResearchCentre,Wuxi
简介:Atime-domainKelvinsourcehigh-orderpanelmethodbasedonNURBSisdevelopedandappliedtosolvetheunsteadywave-makingproblems.Numericalresultsofinstantwaveresistanceandfreesurfaceelevationarepresentedandcomparedwiththeavailabyresultsbyotherauthors,forsubmergedspheroidandspherebeneaththefreesurfaceandforsurfaceshipofWigleymodelsmovingwithunsteadyspeed.Theagreementissatisfying.
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简介:与高精确性提取multipath的参数能被为时间域使用高分辨率的算法完成极端宽带(UWB)隧道建模。干净算法为UWB时间域描述被用作如此的一个高分辨率的算法。这份报纸论述压缩察觉到(CS)为时间域UWB隧道建模基于高分辨率的deconvolution算法。UWB无线隧道是长、稀少的隧道推动反应(CIR)的一个主要例子。而且,仔细匹配multipath的波形的parameterized波形的字典导致UWB隧道测量信号更简洁地被代表。由调整字典的参数,不同分辨率的CIR能被获得。匹配的追求(MP)算法为CS被用作信号重建方法并且直接输出CIR。我们也证明如果CS的字典明确地被设计,MP是单个模板的等价物干净。最后,CS-MP的计算复杂性被分析并且MP的比较并且干净被执行。模拟结果显示出那与相比干净,建议CS-MPdeconvolution算法能与许多少数完成可比较的表演采样。
简介:Severalindolederivativeswithdifferent‘3-'substituentshavebeeninvestigatedbyterahertz(THz)time-domainspectroscopy.Thelow-frequencyabsorptionspectraandrefractiveindiceswereobtainedintherangeof0.2THzto2.5THz(7cm–1to83cm–1).Thesederivativeswithdifferentsubstituentspresentdistinctfeatures,whichsuggeststhatTHzspectroscopyissensitivetodifferentstructuresandcomponentsofthesechemicals.Thedensityfunctionaltheorywasemployedtocalculatethelow-frequencyvibrationalpropertiesofindole-3-carboxylicacidandindole-3-propionicacidbasedontheircrystalstructures,andtheintermolecularinteractionswereinvolved.Meanwhile,thetemperaturedependenceofthespectraagreedwiththecalculatedresults.ThequantitativeanalysisofaternarymixturewasstudiedbytakingtheTHzfingerprintsintoaccount,andtheresultsdemonstrateTHzspectroscopyhasgreatpotentialforthepracticalapplicationsinbiochemistryandpharmaceutics.
简介:Thevibrationandsoundradiationofasubmergedsphericalshellarestudiedinthetime-domainbyLaplacetransformmethod,whereaCWpulseforceactsattheapexoftheshell.Thenumericalresultsforthecaseoflongpulseshowthatthedifferentvibrationalmodesandtheresonantorbeatradiatedsoundareexcitedfordifferentcarrier-frequencies,butlitlesoundisra-diatedforsomevibrationalmodes.Forthecaseofshortpulsethewaveformsofthepulsebecomewidenedanddeformed,whenthepulsepropagatesbetweenapexesoftheshell.Then,theDoublyAsymptoticApproximations(DAA2)andKirchhoff‘sRetardedPotentialFormulate(KRPF)areusedtosolvethesameproblem.ItisshownthattheresultsofDAA2andKRPFmethodhaveagoodagreementwiththeresultsofLaplacetransformmethod.
简介:AnovelandefficienttechniquetodesignmodulateddiscreteFouriertransform(DFT)filterbanksisintroducedinthispaper.Theproposedmethodfirstrelaxesthelimitsthatthesynthesisfiltersarethetime-reversedversionoftheanalysisfiltersandthenadoptsthetimedomainformulaoftheperfectreconstructionpropertyasthesolutiontodesignthesynthesisfilters.TheprototypefilterinanalysisfilterbanksisdesignedbasedonFourier-Kaiserwindowapproach.Simulationresultsshowthatthedesignedfilterbanksapproximatelysatisfytheperfectreconstructionwithcontrollablereconstructionerrors.