简介:摘要近年来人口和小汽车数量的持续增长使得大中型城市的交通拥堵问题日益严重,有限的城市道路资源已不能承受日益增长的交通量。为了缓解交通供给与交通需求之间的矛盾,一系列的交通预测模型和算法应运而生,这些预测模型的建立和算法的运行都是以大量的交通数据为基础的,从而体现了交通数据挖掘研究的重要性。而在交通流运行过程中,道路交叉口作为交通流运行的瓶颈,是导致交通拥堵的关键所在,因此,对路口交通数据的挖掘与研究是提高道路交通运行效率的有效途径之一。
简介:ObjectiveUnderstandingthedynamicsofsedimentgravityflowsisofgreatimportancetocorrectlyinterprettheirrelateddeposits.Thediscoveryofsupercriticalsedimentgravityflowsprovidessomenewviewpointsfortheexplanationofcontroversialsedimentgravityflowdeposits.However,thedynamics,formation,evolutionprocessesofsupercritical
简介:China'sislandandreefcoastsaremainlydistributedalongthecoastsofZhejiangandFujianprovinces.Theseareashavefavorabledeep-waterconditionsandgreatdevelopmentpotential.TheZhoushanArchipelagoisatypicalislandandreefcoast.Inthemidstoftheislands,therearemanytidalchannelswithhighwaterdepthandhighcurrentvelocity.DaishanIslandislocatedonthenorthernpartoftheZhoushanArchipelago.TheseanorthofDaishanIslandcanbecharacterizedashavinggreatwaterdepth(generallybetween10and20m),highcurrentvelocity(themaximummeasuredvalueisabout2m/s),andhyperconcentratedsuspendedsediment(annualaverageconcentrationundernormalweatherconditionsisabout0.6kg/m3).Sedimenttransportisinfluencedbytheco-actionofwavesandcurrents.Landreclamationcaneasethecontradictionbetweenthedesirefordevelopmentandthelandresourceshortageonislandandreefcoasts.Landreclamationgenerallystartsfromdeposition-promotingprojectsonislandandreefcoastswithhyperconcentrationofsuspendedsedimentwiththeaimofreducingthereclamationcost.BasedonthemorphodynamiccharacteristicsoftheseaareanearnorthofDaishanIsland,atwo-dimensionalmathematicalmodelwasdevelopedtoanalyzetheco-actionofcurrentandwavesandthemodelwasverifiedforspringaswellasneaptidesin2007and2012.Thesimulatedvaluesoftidalstages,tidalcurrentvelocities,tidalcurrentdirections,andsuspendedsedimentconcentrationat15stationsin2007and9stationsin2012wereingoodagreementwiththein-situmeasuredvalues.Furthermore,thesimulatedmagnitudeandpatternoferosionandsedimentationagreedwellwiththeobservations.Thismodelwasusedtoevaluatetheeffectsofaproposedsiltationschemeonthehydrodynamicenvironmentandmorphologicalchangeofthestudyarea.Theresultsofthisstudycaninformtheprotection,development,andutilizationofshoal-channelsonislandandreefcoasts,aswellprovideascientific
简介:Disturbancesthatcreategapscanshapethestructureandfunctionofforests.However,suchdisturbanceregimesinAsiantropicalmontanerainforestsremainlargelyunquantified.Leaststudiedaretyphoondisturbancesthatareattributabletoclimatechange.Weinvestigatedgapcharacteristicsintermsofsize,age,andgapmakertoquantifythegapdisturbanceregimesinanintactold-growthtropicalmontanerainforestonHainanIsland,China.Theintensityoftyphoonshasincreasedsince1949,andtyphoonwindsblowmostly(45.5%)fromthenortheastcornerofHainanIsland,resultinginahigherfrequencyofgapsinthenortheast.Atotalof221gap-makers(treesthatfelltocreatecanopygaps)and53gapswereobservedina3.16haold-growthrainforest.Mostcanopygaps(85%)were\200m2.Theaveragesizeofcanopygapswassmallerintherainforestthaninothertropicalforests,whiletheaveragesizeofexpandedgapswassimilartothoseinothertropicalforests.Themaximumageofgapswas23.5yearsindicatingthatgapshadmorerapidturnoverthanotherpartsoftropicalforests.Thefrequencydistributionofgap-makersfollowedalognormaldistributionwithadistinctivepeakatthreegap-makers,whichwasdifferentfromtheinverseJ-shapedcurvetypicalofothertropicalforests.Gapswererecordedmainlyonslopesbetween20_and35_andwooddensityofgap-makerswasbetween0.6and0.7gcm-3.Ourresultssuggestthatsmall-scaledisturbancewasthedominantagentofgapformationinthisold-growthrainforestthatissubjecttoincreasingtyphoondisturbances.