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简介:Background:Conceptualmodelsofforestdynamicsarepowerfulcognitivetools,whichareindispensableforcommunicatingecologicalideasandknowledge,andindevelopingstrategicapproachesandsettingtargetsforforestconservation,restorationandsustainablemanagement.Forestdevelopmentthroughtimeisconventionallydescribedasadirectional,or'linear',andpredictablesequenceofstagesfrom'bareground'tooldforestrepresentingthe'climax-state'.However,thissimpleviewisincompatiblewiththecurrentknowledgeandunderstandingofintrinsicvariabilityofforestdynamics.Hypothesis:Overlysimpleconceptualmodelsofforestdynamicseasilybecometransformedintobiasedmentalmodelsofhowforestsnaturallydevelopandwhatkindofstructurestheydisplay.Tobeabletocommunicatetheessentialfeaturesanddiversityofforestdynamics,comprehensiveconceptualmodelsareneeded.Forthisend,Kuuluvainen(2009)suggestedarelativelysimpleconceptualmodelofforestdynamics,whichseparatesthreemajormodesofforestdynamics,andincorporatesstatechangesandtransitionsbetweentheforestdynamicsmodesdependingonchangesindisturbanceregime.Conclusions:Conceptualmodelsofforestdynamicsshouldbecomprehensiveenoughtoincorporatebothlongtermdirectionalchangeandshort-termcyclicforestdynamics,aswellastransitionsfromonedynamicsmodetoanotherdependingonchangesinthedrivingdisturbanceregimetype.Modelsthatcapturesuchessentialfeaturesofforestdynamicsareindispensableforeducationalpurposes,insettingreferenceconditionsandindevelopingmethodsinforestconservation,restorationandecosystemmanagement.
简介:Thispaperdealswiththevectorcontrol,includingboththedirectvectorcontrol(DVC)andtheindirectvectorcontrol(IdVC),ofinductionmotors.ItiswellknownthattheestimationofrotorfluxplaysafundamentalroleintheDVCandtheestimationofrotorresistanceisvitalintheslipcompensationoftheIdVC.Intheseestimations,theprecisionissignificantlyaffectedbythemotorresistances.Therefore,onlineestimationofmotorresistancesisindispensableinpractice.Forafastestimationofmotorresistances,itisnecessarytoslowdowntheconvergencerateofthecurrentestimate.Ontheotherhand,forafastestimationoftherotorflux,itisnecessarytospeedupitsconvergencerate.Itisverydifficulttorealizesuchatrade-offinconvergenceratesinafullorderobserver.Inthispaper,weproposetodecouplethecurrentobserverfromthefluxobserversoastorealizeindependentconvergencerates.Then,theresistanceestimationalgorithmisappliedtobothDVCandIdVC.Inparticular,intheapplicationtoIdVCthefluxobserverneedsnotbeused,whichleadstoasimplerstructure.Meanwhile,independentconvergenceratesofcurrentobserverandfluxobserveryieldanimprovedperformance.Asuperiorperformanceinthetorqueandfluxresponsesinbothcasesisverifiedbynumeroussimulations.
简介:本文给出了重新启动的LGMRES方法的一种代价更小的实现方式。这种做法基于消除以下减慢收敛速度的现象:重新启动的simplerGMRES的每次循环结束时得到的残向量经常交替方向,与重新启动的GMRES的情形类似。这种新的变形的方法的优点是它比重新启动的LGMRES所需要的计算量要少,大量的例子表明该方法计算速度更快。