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简介：Aerodynamicforcesandpowerrequirementsinforwardflightinabumblebee(Bombusterrestris)werestudiedusingthemethodofcomputationalfluiddynamics.Actualwingkinematicdataoffreeflightwereusedinthestudy(thespeedrangesfrom0m/sto4.5m/s;advanceratiorangesfrom0-0.66).Thebumblebeeemploysthedelayedstallmechanismandthefastpitching-uprotationmechanismtoproduceverticalforceandthrust.Theleading-edgevortexdoesnotshedinthetranslatoryphaseofthehalf-strokesandismuchmoreconcentratedthanthatofthefruitflyinapreviousstudy.Athoveringandlow-speedflight,theverticalforceisproducedbyboththehalf-strokesandiscontributedbywinglift;atmediumandhighspeeds,theverticalforceismainlyproducedduringthedownstrokeandiscontributedbybothwingliftandwingdrag.Atallspeedsthethrustismainlyproducedintheupstrokeandiscontributedbywingdrag.Thepowerrequirementatlowtomediumspeedsisnotverydifferentfromthatofhoveringandisrelativelylargeatthehighestspeed(advanceratio0.66),i.e.thepowercurveisJshaped.Exceptatthehighestflightspeed,storingenergyelasticallycansavepowerupto20%-30%.Atthehighestspeed,becauseofthelargeincreaseofaerodynamictorqueandtheslightdecreaseofinertialtorque(duetothesmallerstrokeamplitudeandstrokefrequencyused),thepowerrequirementisdominatedbyaerodynamicpowerandtheeffectofelasticstorageofenergyonpowerrequirementislimited.

简介：Researchonparticulatecharacteristicshasbeenanimportantfrontierinphysicsandchemistryduringthepastdecades.Ithashoweverbeenmostlyfocusedongranularmaterialswithshort-rangeinteractions.Inthiswork,itwasfoundthatthepowerlawofparticlesizedistributionappliedtothelong-rangeinteractingsystemoffloatingdustinair,fromwhichwededucedthatself-organizedcriticalitymightholdforfloatingdustjustasgranularmaterialswithshort-rangeinteractions.Thisfeaturemayrevealunderlyingkineticmechanisms,importantindispersedparticlesystems.Inindustry,powerlawofsizedistributionofdispersedparticlescanbeusedtoinvestigatethechangeofdustsize,andthepowerlawparametercouldbetakenasanimportantindexfordustseparation.

简介：Animprovedsmoke-wireflowvisualizationtechniqueusingalargecapacitorasthepowersourcewasproposed.Electriccurrentdischargedfromcapacitorswasusedtoheatafinemetalwiresuspendedintheflowfield.Theoildropletsattachedtothewirewerevaporizedandsmokefilamentsfollowedtheflowmotions.Adigitalcamerawasusedtorecordtheimagesofthesmokefilaments.Theactionsofdischargingandcamerashutterweretriggeredbysignalsfromamicrocontrollertoensuretheaccuratetiming.Clearimagesofthestreaklineswerecapturedatafreestreamvelocityupto12.9m/s,muchhigherthanthelimitsoftheexistingtechniques.

简介：InteractionbetweentwosphereswithaninterstitialfluidisessentialinDiscreteElementmodelingforsimulatingthebehaviorsof'wet'particulatematerials.InthispapertheinteractionbetweentwosphereswithaninterstitialPower-lawfluidwasapproximatelyresolvedasnormalandtangentialinteractivemodelsrespectively,forwhichthegoverningequationsweresimplifiedonthebasisofReynoldsapproximation.Theseequationswerethensolvedanalyticallytogetherwiththeboundaryconditionstoobtainthepressuredistributionsforeachindividualmodel,andeventuallysolutionsoftheviscoussqueezeforceandthetangentialviscousresistancewereobtained,whichprovideasetofsolutionsforimplementingintoDEMcodeorotherpurposes.

简介：在与喉咙直径的一张超声的嘴相结合的一个低动力的弧气体加热器的流动不到1mm相当复杂、困难在量的详细描述。单原子的气体氩和氦的加热弧的超声的喷气推进器的实验被执行了，他们的表演测量了。流动特征在数字模拟的帮助下被分析。结果证明粘滞效果是引起理想、真实的性能之间的大差别的最重要的因素。出口流动的大外部节是慢吞吞的。这在氦是特别显著的，在嘴的70%出口区域可能在亚声的流动的地方。磨擦力量能比网推进的大得多，在氦更高若干次到达，导致很低的效率。引起理想、真实的流动之间的差别的另外的因素包括：在喉咙区域，延长到嘴扩大节的电的弧，到入口气体并且从热血浆的热转移，和在真空房间的环境压力的复杂流动。当处理如此的复杂状况时，超声的嘴流动的平常的概念必须极大地被修改，这被认出当处理如此的复杂状况时。在这份报纸介绍的一般概念能在指导这台设备的设计和操作是有用的。

简介：Thesteadytwo-dimensionalmagnetohydrodynamicstagnationflowtowardsanonlinearstretchingsurfaceisstudied.Theno-slipconditiononthesolidboundaryisreplacedwithapartialslipcondition.Ascalinggrouptransformationisusedtogettheinvariants.Usingtheinvariants,athird-orderordinarydifferentialequationcorrespondingtothemomentumisobtained.Ananalyticalsolutionisobtainedinaseriesformusingahomotopyanalysismethod.Reliabilityandefficiencyofseriessolutionsareshownbythegoodagreementwithnumericalresultspresentedintheliterature.Theeffectsoftheslipparameter,themagneticfieldparameter,thevelocityratioparameter,thesuctionvelocityparameter,andthepowerlawexponentontheflowareinvestigated.Theresultsshowthatthevelocityandshearstressprofilesaregreatlyinfluencedbytheseparameters.

简介：Thefatiguebehaviorofahighstrengthsteel300Minthegigacycleregimewasinvestigated.Fullyreversedtension-compressionfatiguetestsatambienttemperaturewereperformedusinganultrasonicfatiguesystemoperatingat20kHz.Thestaircasetestmethodwasemployedtoobtainaccuratevaluesofthemeanfatiguestrengthcorrespondingtofixednumbersofcyclesupto10~9.Theseresultswerecomparedtothecurvewhichisestimatedbythedatatestedinthemid-longliferegimeonconventionalservohydraulictestmachineat20Hz.Resultsindicatethatthefatiguestrengthdeterminedfromultrasonicfatiguetestingislightlyhigherthanconventionaltestingintherangeof10~6-10~7cycles.Itisobviousthatnucleationsoffracturestendtooccurbelowthesurface,iffractureshappenaftermorethan10~7cycles.AllthefracturedspecimensfailsfrominternalSiO_2inclusionsorsmallercarbidesandcarbideclusters.

简介：Synchronousgammaoscillationsarebelievedtoplayaprominentroleintheinformationprocessingofbiologicalneuralsystems.Experimentalobservationshavefoundthatthefrequencyandpowerofgammaoscillationsintheprimaryvisualcortex(V1zone)areregulatedbytheilluminationcontrastofvisualstimulus.However,theunderlyingmechanismofhowthesynchronousoscillationsdependontheilluminationcontrasthasnotbeenwellexplained.Weproposealocalexcitatory/inhibitory(E/I)neuronalnetworkofintegrate-and-fire(IAF)neuronswiththedifference-of-Gaussians(DOG)receptivefieldtounveilthismechanism.Simulationresultsdemonstratethatthehighertheilluminationcontrast,thehigherthefrequencyofgammaoscillations.Thepowerofgammaoscillationsalsoincreaseswiththeincreaseofilluminationcontrast.Theseresultsareconsistentwiththeexperimentalfindings.

简介：电影动量和在加速上的薄有限幂定律液体的热运输特征上的内部加热来源的效果不稳定的水平拉长的接口被学习。不同于这块地里的很古典的工作，为改变热电导率的液体电影和概括Fouriers法律的一般表面温度分布被考虑。适当类似转变被用来与一组二点的平常的微分方程(颂诗)把强烈非线性的管理部分微分方程(PDE)变换成一个边界价值问题。在液体电影厚度和摇摆参数之间的通讯在MATLAB用BVP4C节目被导出。自我类似颂诗的数字答案用与一个Runge-Kutta重复程序和牛顿计划相结合的射击技术被获得。液体上的深奥物理参数的效果水平速度和温度分发被介绍并且讨论。

简介：Inthepresentpaper,thecompatibilityequationfortheplanestressproblemsofpower-lawmaterialsistransformedintoabiharmonicequationbyintroducingtheso-calledcomplexpseudo-stressfunction,whichmakesitpossibletosolvetheelastic-plasticplanestressproblemsofstrainhardeningmaterialsdescribedbypower-lawusingthecomplexvariablefunctionmethodlikethatinthelinearelasticitytheory.Byusingthisgeneralmethod,theclose-formedanalyticalsolutionsforthestress,strainanddisplacementcomponentsoftheplanestressproblems’ofpower-lawmaterialsisdeducedinthepaper,whichcanalsobeusedtosolvetheelasto-plasticplanestressproblemsofstrain-hardeningmaterialsotherthanthatdescribedbypower-law.Asanexample,theproblemofapower-lawmaterialinfiniteplatecontainingacircularholeunderuniaxialtensionissolvedbyusingthismethod,theresultsofwhicharecomparedwiththoseofaknownasymptoticanalyticalsolutionobtainedbytheperturbationmethod.

简介：基于Sigma-deltaModulator（Σ△M）原理的数字闭环微机械加速度计不仅实现了力反馈闭环控制,同时直接完成信号的模数转换。基于全差分式电容微加速度设计了一种2-2级联式（MASH）高阶Σ△M闭环系统——MASH_（2-2）,并与传统的单环路二阶、四阶Σ△M闭环系统（SD2、SD4）进行了仿真分析比较,研制了原理样机。微加速度计是基于结构层厚度50mm的SOI硅片通过DRIE刻蚀、气态HF释放等一系列微加工工艺得到,系统电路以数字化方式集成在FPGA中。常压下测试结果表明,样机的灵敏度为0.876V/g,噪声基底为-110dB,零偏不稳定性为20mg,静态温漂为40.8mg/℃,量程为±20g。

简介：实验研究复杂波形结构引起平面界面变形和反射激波冲击下的R-M不稳定性的问题.在竖直激波管中生成稳定的N2/SF6平面界面,激波在圆柱绕射后,冲击平面界面,由此研究复杂激波引起的界面变形.平面激波在圆柱绕射后的流场,演化成具有初始入射波、三波点、弯曲反射波、Mach波和Mach反射产生的滑移线等复杂结构.研究复杂结构激波对界面的作用,对认识界面扰动的生成具有较大帮助.绕柱激波冲击后,平面界面仅在两对滑移线内部发生变形.绕柱激波冲击界面后,两对滑移线将界面分成＂内界面＂和＂外界面＂,界面变形形态同滑移线和界面相交位置相关.反射激波二次冲击下,界面扰动的增长与Jacobs-Sheeley涡量模型较吻合.

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.

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