简介:Inthisarticle,westudytheexplicitexpressionsoftheconstantsintheerrorestimateofthenonconformingfiniteelementmethod.WeexplicitlyobtaintheapproximationerrorestimateandtheconsistencyerrorestimatefortheWilson'selementwithouttheregularassumption,respectively,whichimpliesthefinalfiniteelementerrorestimate.Suchexplicitapriorierrorestimatescanbeusedascomputableerrorbounds.
简介:Theoptimizationdesignofthepowersystemisessentialforstratosphericairshipswithparadoxicalrequirementsofhighreliabilityandlowweight.Themethodologyoforthogonalexperimentispresentedtodealwiththeproblemoftheoptimizationdesignoftheairship’spowersystem.Mathematicalmodelsofthesolararray,regenerativefuelcell,andpowermanagementsubsystem(PMS)arepresented.Thebasictheoryofthemethodoforthogonalexperimentisdiscussed,andtheselectionoffactorsandlevelsoftheexperimentandthechoiceoftheevaluationfunctionarealsorevealed.TheproposedmethodologyisvalidatedintheoptimizationdesignofthepowersystemoftheZhiYuan-2stratosphericairship.Resultsshowthattheoptimalconfigurationiseasilyobtainedthroughthismethodology.Furthermore,theoptimalconfigurationandthreesub-optimalconfigurationsareintheParetofrontierofthedesignspace.Sensitivityanalysesfortheweightandreliabilityoftheairship’spowersystemarepresented.
简介:Lithiumsulfurbattery(LSB)offersseveraladvantagessuchasveryhighenergydensity,low-cost,andenvironmental-friendliness.However,itsuffersfromseriousdegradationofitsreversiblecapacitybecauseofthedissolutionofreactionintermediates,lithiumpolysulfides,intotheelectrolyte.Tosolvethislimitation,therearemanystudiesusinggraphene-basedmaterialsduetotheirexcellentmechanicalstrengthandhighconductivity.Comparedwithgraphene,grapheneoxide(GO)containsvariousoxygenfunctionalgroups,whichenhancethereactionwithlithiumpolysulfides.Here,weinvestigatedthepositiveeffectofusingGOmixedwithcarbonblackontheperformanceofcathodeinLSB.WehaveobservedasmallerdropofcapacityinGOmixedsulfurcathode.Wefurtherdemonstratethatthemechanisticoriginofreversibilityimprovement,asconfirmedthroughCVandRamanspectra,canbeexplainedbythestabilizationofsulfurinlithiumpolysulfideintermediatesbyoxygenfunctionalgroupsofGOtopreventdissolution.Ourfindingssuggestthattheuseofgrapheneoxide-basedcathodeisapromisingroutetosignificantlyimprovethereversibilityofcurrentLSB.
简介:AmethodtoidentifycomplexYoung’smodulusofviscoelasticmaterialsusingforcedlongitudinalvibrationofslenderrodsisproposed.Themethoddiffersfromthebeamone.Experimentaltestswerecarriedoutatroomtemperaturewithdifferentlengthsin108mm,100mm,90mm,83.5mm,80mm.74.5mm,70mmforthepolycarbonatebars,andthecurvesofratiosA2/A1betweentwoendsofaviscoelasticbarversusfrequenciesareobtained,furthermore,thecorresponding3dBbandwidthandthestorageandlossmoduluscanbecalculated.SufficientnumberofobtainedcomplexYoung’smodulusatdifferentfrequencyallowsustocalculateotheronesusingtheleastsquaremethod.Ifthestepofthetestedfrequencyis5Hz,themaximumerrorofresultscanbelessthan6%.Bycomparisonwiththemeasurementmethodswhichthepreviousliteraturementioned,thisnewmethodsimplifiesthecalculation,andthephysicalmeaningappearsapparentlyandclearly.
简介:Micro-mesoporouscompositemolecularsievesH-ZSM-5/MCM-41werepreparedbythehydrothermaltechniquewithalkali-treatedH-ZSM-5zeoliteasthesourceandcharacterizedbyscanningelectronmicroscopy,transmissionelectronmicroscopy,energydispersivespectroscopy,X-raydiffraction,N2adsorption-desorptionmeasurementandNH3temperature-programmeddesorption.ThecatalyticperformancesforthemethanoldehydrationtodimethyletheroverH-ZSM-5/MCM-41wereevaluated.Amongthesecatalysts,H-ZSM-5/MCM-41preparedwithNaOHdosage(nNa/nSi)varyingfrom0.4to0.47presentedexcellentcatalyticactivitywithmorethan80%methanolconversionand100%dimethyletherselectivityinawidetemperaturerangeof170—300℃,andH-ZSM-5/MCM-41preparedwithnNa/nSi=0.47showedconstantmethanolconversionofabout88.7%,100%dimethyletherselectivityandexcellentlifetimeat220℃.Theexcellentcatalyticperformanceswereduetothehighlyactiveanduniformacidicsitesandthehierarchicalporosityinthemicro-mesoporouscompositemolecularsieves.ThecatalyticmechanismofH-ZSM-5/MCM-41forthemethanoldehydrationtodimethyletherprocesswasalsodiscussed.
简介:Removalofcarbonylsulfide(COS)fromCO2streamissignificantfortheproductionandutilizationoffoodgradeCO2.ThisstudyinvestigatestheadsorptionperformanceofAg/NaZSM-5asadsorbentpreparedbyincipientwetnessimpregnationfortheremovalofCOSfromaCO2streaminafixed-bedadsorptionapparatus.Effectsofvariousconditionsonthepreparationofadsorbent,adsorptionanddesorptionwereintensivelyexamined.TheresultsrevealedthatCOScanberemovedtobelow1×10-9fromaCO2stream(1000ppmCOS/CO2)usingAg/NaZSM-5(10wt%AgNO3)withanadsorptioncapacityof12.86mg·g-1.Theadsorbentcanbefullyregeneratedusinghotairat450C.Theadsorptionabilityremainedstableevenaftereightcyclesofregeneration.
简介:Westudyboundaryvalueproblemsforfractionalintegro-differentialequationsinvolvingCaputoderivativeoforderα∈(n-1,n)inBanachspaces.ExistenceanduniquenessresultsofsolutionsareestablishedbyvirtueoftheHolder'sinequality,asuitablesingularGronwall'sinequalityandfixedpointtheoremviaaprioriestimatemethod.Atlast,examplesaregiventoillustratetheresults.
简介:DrivenbycuriosityaboutpossibleflightoptionsfortheChang’e-2spacecraftafteritremainsattheSun-EarthL2point,effectiveapproachesweredevelopedfordesigningpreliminaryfuel-optimalnear-Earthasteroidflybytrajectories.Theapproachesincludetheuseofmodifiedunstablemanifolds,gridsearchofthemanifolds’parameters,andatwo-impulsemaneuverfororbitalphasematchingandz-axisbiaschange,andaredemonstratedtobeeffectiveinasteroidtargetscreeningandtrajectoryoptimization.Asteroidflybysareexpectedtobewithinadistanceof2×107kmfromtheEarthowingtotheconstrainedEarth-spacecraftcommunicationrange.Inthiscase,thespacecraft’sorbitalmotionissignificantlyaffectedbythegravitiesofboththeSunandtheEarth,andtherefore,theconceptofthe"heliocentricoscillating-Keplerorbit"isproposed,becausetheclassicalorbitalelementsoftheflybytrajectoriesreferencedintheheliocentricinertialframeoscillatesignificantlywithrespecttotime.Theanalysisandresultspresentedinthisstudyshowthat,amongtheasteroidswhoseorbitsarethemostaccuratelypredicted,"Toutatis","2005NZ6",or"2010CL19"mightbeencounteredbyChang’e-2inlate2012or2013withtotalimpulseslessthan100m/s.
简介:Directconversionoffructose-basedcarbohydratesto5-ethoxymethylfurfural(EMF)catalyzedbyLewisacidinethanolwasinvestigated.ItwasfoundthatBF3(Et)2Owasfavorablefor5-hydroxymethylfurfural(HMF)etherificationtoEMF.BF3(Et)2OcombinationwithAlCl36H2Owiththemolarratioof1wasaneffectivecatalystsystemforsynthesisofEMFfromfructose-basedcarbohydrates.55.0%,45.4%and23.9%ofEMFyieldswereobtainedfromfructose,inulinandsucroseunderoptimizedconditions,respectively.