学科分类
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3 个结果
  • 简介:Differentfrombirdsandinsects,batshavecomplexwing-deformationcapacitytogeneratehighaerodynamicforces.Inflight,theactivelymorphingofbatwingincludesthetwistingfromwingroottowingtip,thecamberingalongthechordwisedirection,thebendingalongthespanwisedirectionandthewingarea-changingcausedbythestretchandretractionofthewingspan.Itwasfoundthatthehighthrustandliftrequiredinbatflightaredependentonthewingtwistingandcamberingrespectively.Moreover,theintegratedwing-morphinggeneratestheaerodynamicliftandthrustmainlyduringthedownstrokeandalmostnegligibleforcesduringtheupstroke.Thewingarea-changingandbendingcanbeusedtoamplifythepositiveforcesinthedownstrokedurationandreducethenegativeforcesintheupstrokeduration.

  • 标签: 空气动力学 变形能力 蝙蝠 学习 持续时间 机翼
  • 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.

  • 标签: Gamma oscillations ILLUMINATION CONTRAST E/I network
  • 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.

  • 标签: 近地小行星 飞行轨迹 地球 太阳 轨道运动 不稳定流形