简介:ElectrondensityisakeyparametertocharacterizeMartianionosphericstructureanddynamics.BasedontheephemerisandauxiliaryinformationderivedfromtheSpacecraft,Planet,Instruments,C-matrix,andEvents(SPICE)toolkit,wecalculatedthebendingangleofsignalpathfromthefrequencyresidualsmeasuredbytheMarsExpressRadioScienceExperiment(MaRS)oftheMarsExpress(MEX)missionundertheassumptionofasphericallysymmetricionosphere.Westratifiedtheionosphereintolayersandassumedalinearchangeofbendinganglebetweenlayers,toderiveprofilesinradialdistanceofrefractivitywiththeoptimizedparametersofupperintegrallimitof4890kmandbaselinecorrectionboundaryof3690km.Meanwhile,wealsocomparedtheretrievedelectrondensityprofilesbetweenthefrequencyresidualsofthesingle-frequencyanddifferentialDopplerofthedual-frequency.Intotal,~640electrondensityprofilesofMartianionospherebetweenApril2004andApril2015wereretrievedsuccessfully.Thereare24profilesidentifiedmanuallythatexhibitanadditionalsporadiclayeroccurrencebelowthenormaltwo-layers.Wealsofoundthatthepeakaltitudeofthislayerincreaseswiththemainpeakaltitude.
简介:近20a来,人工湿地系统由于具有独特的净化机理和功能而越来越多地被用于处理生活污水、工业废水和农业污水.人工湿地系统之所以受到国际上广泛的关注,这是由于它具有低能耗,低成本,运行费用少和操作简便等优势.湿地植物在人工湿地中起着非常重要的作用,不但可以直接摄取和利用污水中的营养物质、吸收富集污水中的重金属等有毒有害物质;而且还能输送氧气到根区,提供根区微生物生长、繁殖和降解过程中对氧的需求.通过详细阐述植物对水中营养元素的吸收作用,说明了植物在人工湿地处理污水中的重要性,并提出了一些改进人工湿地处理污水能力的设想以及人工湿地系统水生植物有待进一步研究的问题,研究结果可以为进一步优化人工湿地系统的设计提供参考.