简介:通过对市场结构理论演变过程的回顾,认为以SCP范式为基础的传统市场结构分析框架越来越不适应于当前日益复杂的经济环境。基于此,本文提出了网络型市场结构的概念,分析了网络型市场结构的特征,讨论了网络结构型市场结构的分类,并提出了网络型市场结构的一般模式。接着,构建了网络型寡头垄断市场结构模型,分析了该模型的四个特性。之后,对2×2网络型寡头垄断市场结构存在的八种策略组合进行了合并整理,求出了在现实中经常采用的四种不同的策略组合下的Cournot产量均衡解、价格均衡解以及实现均衡时的利润。最后,通过一个算例对各个Cournot均衡解的特性进行了分析,并比较了四种策略组合的优劣。
简介:WepresentthetemperaturedependentelectricaltransportmeasurementsofAg/Si(111)-(√3×√3)R30°bytheinsitumicro-four-pointprobemethodintegratedwithscanningtunnelingmicroscopy.Thesurfacestructurecharacterizationsshowhexagonalpatternsatroomtemperature,whichsupportstheinequivalenttriangle(IET)model.Ametal-insulatortransitionoccursat-115K.Thelowtemperaturetransportmeasurementsclearlyrevealthestronglocalizationcharacteristicsoftheinsulatingphase.
简介:建立了电感耦合等离子体发射光谱法测定镍铬合金中Si,Mn,Fe,Ti,A1,Cu元素含量的分析方法。确定了溶样方法和分析谱线,采用基体匹配消除干扰。对方法精密度和准确度进行实验,实验结果表明,各元素的相对标准偏差均小于3%,加标回收率在86.8%~106.9%,镍铬合金标准物质的各元素测定结果均与标准值一致。所建立的方法快速、准确,适用于镍铬合金中多元素同时测定。
简介:Inthiswork,MoOxpromotedIr/SiO2catalystswerepreparedandusedfortheselectivehydrogenolysisoftetrahydrofurfurylalcohol(THFA)to1,5-pentanediolinacontinuousflowreactor.Theeffectsofdifferentnoblemetals(Ir,Pt,Pd,Ru,Rh),supportsandIrcontentswerescreened.Amongtheinvestigatedcatalysts,4wt%Ir-MoOx/SiO2withaMo/Iratomicratioof0.13exhibitedthebestcatalyticperformance.ThesynergybetweenIrparticlesandthepartiallyreducedisolatedMoOxspeciesattachedonthemisessentialfortheexcellentcatalyticperformanceofIr-MoOx/SiO2.ThecatalystexhibitedabetterhydrogenolysisefficiencyofTHFAwiththeselectivityof1,5-pentanediolof65%–74%ataconversionofTHFAof70%–75%whentheinitialTHFAconcentrationisrangingfrom20wt%and40wt%.AndhighersystempressurewasalsoinfavoroftheconversionofTHFA.Duringastabilitytest,theconversionofTHFAand1,5-pentanediolyieldoverIr-MoOx/SiO2decreasedwithreactiontime,whichcanbeexplainedbytheleachingofMospeciesduringthereaction.
简介:ThecrystalstructureofDi-nitratobis(ethylcaprolactam)uranyl(Ⅱ)UO2[CH2(CH2)4CONC2H5]2(NO3)2wasestablishedbyasingle-crystalX-raydiffractionstudy.Itistriclinie,spacegroupP1,witha=7.171(2),b=8.655(3),c=10.182(5)A,α=78.27(3),β=70.63(3),γ=81.76(3)°,V=581.7(4)A3,Z=l,Dc=1.94g.cm-3.FinalRvalueis0.0218.Theresultrevealsthaturanylioniscoordinatedtosixoxygenatoms,twoofthemarefromtwocarbonylgroupsofethylcaprolactamandtheotherfourarefromtwonitrategroups.
简介:受限混合层的流动主要是喷流与自由来流相互剪切形成的混合层受到壁面的限制而形成的一种流动.文章采用后向台阶平板模型研究了高速高压比条件下的受限混合层的典型流场结构以及冷却效率.实验自由来流Mach数为5,喷流的Mach数为1.28,喷流总压为0.2~0.7MPa,通过调整冷喷气流的总压,基于纹影流动显示技术获得喷口附近的激波结构特征和流动参数之间的关系.形成喷口附近波系的欠膨胀流动现象的深刻认识,提取波系特征与流动参数之间的规律.基于流动显示及实验测量结果,通过分析流场中大尺度结构的空间演化规律,揭示流动参数对于冷却效率的影响规律及物理内涵.采用快响应压敏漆(FRPSP)技术在高超声速风洞开展热流分布和冷却效率研究,获得了平板对受限混合层冷却效率的影响.
简介:在磷酸钠-磷酸二氢铵-高锰酸钾体系中对镁合金进行化学转化处理.研究了磷酸钠、磷酸二氢铵、高锰酸钾、温度、时间和添加剂对转化膜性能的影响.通过对转化膜结构、成分及性能的测试评价,得到了性能较好的化学转化溶液配方:Na3PO4为5g·L^-1,NH4H2PO4为15g·L^-1,KMnO4为1g·L^-1,添加剂(NH4)5Mo7O24为0.5g·L^-1.由SEM可观察到转化膜的表面成“干枯河床”状.XRD和EDS检测表明,膜层的主要成分是Mg,Al12Mg17和无定形相,膜层表面主要有Mn,Mg,K,O和Al等元素组成.腐蚀实验和电化学测试表明,添加剂能够降低转化膜的腐蚀率,转化膜较基体的腐蚀电位正移了0.73V,提高了镁合金的耐蚀性.
简介:Thispaperpresentedacontroldesignmethodologyforaprotonexchangemembranefuelcell(PEMFC)generationsystemforresidentialapplications.Thedynamicbehaviorofthegenerationsystemiscomplexinsuchapplications.Acomprehensivecontroldesignisveryimportantforachievingasteadysystemoperationandefficiency.Thecontrolstrategyfora60kWgenerationsystemwasproposedandtestedbasedonthesystemdynamicmodel.Atwo-variablesingleneuronproportional-integral(PI)decouplingcontrollerwasdevelopedforanodepressureandhumiditybyadjustingthehydrogenflowandwaterinjection.Asimilarcontrollerwasdevelopedforcathodepressureandhumiditybyadjustingtheexhaustflowandwaterinjection.Thedesiredoxygenexcessratiowaskeptbyafeedbackcontrollerbasedontheloadcurrent.Anoptimalseekingcontrollerwasusedtotracetheuniqueoptimalpowerpoint.TwonegativefeedbackcontrollerswereusedtoprovideACpowerandasuitablevoltageforresidentialloadsbyapowerconditioningunit.Controlsimulationtestsshowedthat60kWPEMFCgenerationsystemrespondedwellforcomputer-simulatedstepchangesintheloadpowerdemand.Thiscontrolmethodologyfora60kWPEMFCgenerationsystemwouldbeacompetitivesolutionforsystemleveldesignssuchasparameterdesign,performanceanalysis,andonlineoptimization.
简介:Inthispaper,a60kWprotonexchangemembranefuelcell(PEMFC)generationsystemismodeledinordertodesignthesystemparametersandinvestigatethestaticanddynamiccharacteristicsforcontrolpurposes.Toachieveanoverallsystemmodel,thesystemisdividedintofivemodules:thePEMFCstack(anodeandcathodeflows,membranehydration,andstackvoltageandpower),cathodeairsupply(aircompressor,supplymanifold,cooler,andhumidifier),anodefuelsupply(hydrogenvalveandhumidifier),cathodeexhaustexit(exitmanifoldandwaterreturn),andpowerconditioning(DC/DCandDC/AC)modules.Usingacombinationofempiricalandphysicalmodelingtechniques,themodelisdevelopedtosettheoperationconditionsofcurrent,temperature,andcathodeandanodegasflowsandpressures,whichhavemajorimpactsonsystemperformance.Thecurrentmodelisbasedona60kWPEMFCpowerplantdesignedforresidentialapplicationsandtakesaccountoftheelectrochemicalandthermalaspectsofchemicalreactionswithinthestackaswellasflowsofreactantsacrossthesystem.Thesimulationtestsshowthatthesystemmodelcanrepresentthestaticanddynamiccharacteristicsofa60kWPEMFCgenerationsystem,whichismathematicallysimpleforsystemparametersandcontroldesigns.
简介:TheconstructionofadsorptivetypeC60modifiedelectrodeanditselectrochemicalreductionandoxidationbehaviorinaqueoussolutionsaredescribedinthisreport.Fourpairsofone-electrontransferreductionandoxidationcyclicvoltammetryisobtainedinaqueoussolutioncontaining30%CH3CNand2%(C2H5)4NOH.ItisreportedinthispaperthattheC60modifiedelectrodealsocatalyzestheelectrochemicalreductionofdissolvedoxygenin40%DMFand2%(C2H5)4NOHaqueoussolutionandthismightopenanewfieldforthepotentialapplicationsofC60inelectrochemistryandelectroaualyticalchemistry.
简介:铍为脆性材料,在焊接时容易使焊缝开裂。为了防止焊缝开裂,途径之一是加延展性比较好的金属或合金(如Al-Si合金或银等)作填充材料进行钎接焊。但是,铍在非真空条件下焊接,在焊缝中出现的主要缺陷是焊接气孔和缩孔。人们早已知道,纯铝在焊接或铸造时的加热过程中会吸收环境中的氢,冷却时熔体要释放氢从而形成以氢为特征的氢气孔,进而影响铝加工的质量。这表明铝及铝合金焊接形成的气孔主要是与焊接时熔体的氢含量有关。那么,在加Al-Si合金焊接铍时,产生的气孔是否也与氢含量的关系,Al-Si合金熔体随温度升高氢含量有何变化趋势,Al-Si合金中的Si对铝熔体的吸氢起何作用。