简介:诺姆·乔姆斯基(NoamChomsky)是美国麻省理工学院教授,转换生成语法的创始人,是举世公认的著名语言学家、哲学家和当代认知科学之父。他于1957年创立转换生成理论,世界范围内影响巨大,并以此改变了语言学理论的发展走向。多年来,乔姆斯基对中国的外语教育极为关注,尤其重视与国家基础教育实验中心外语教育研究中心的理论探讨,他以电子邮件的方式解答了语言教学理论与实践方面的诸多问题。该访谈个别之处包含纯语言学知识,略显深奥一点,广大英语教师通过深入阅读,仍然能够较好地理解外语教学的理念、方法、教师、学习者、教学资源等内容,以达到融会贯通之目的。本刊现将最近十余年的访谈汇集、整理,冠以如下题目,分两期刊出,以飨读者。
简介:Lithiation-inducedplasticityisakeyfactorthatenablesSielectrodestomaintainlongcyclelifeinLi-ionbatteries.Westudytheplasticityofvariouslithiatedsili-conphasesbasedonfirst-principlescalculationsandiden-tifythelineardependenceoftheequivalentyieldstressonthehydrostaticpressure.Suchdependencemaycausethecompression-tensionasymmetryinanamorphousSithinfilmelectrodefromalithiationtodelithiationcycle,andleadstosubsequentratchetingoftheelectrodeaftercycliclithiation.Weproposeayieldcriterionofamorphouslithi-atedsiliconthatincludestheeffectsofthehydrostaticstressandthelithiationreaction.Wefurtherexaminethemicro-scopicmechanismofdeformationinlithiatedsiliconundermechanicalload,whichisattributedtotheflow-defectsmediatedlocalbondswitchingandcavitation.Hydrostaticcompressionconfinestheflowdefectsthuseffectivelystrength-enstheamorphousstructure,andviceversa.
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:Epigastricpain,alsoknownasstomachpain,ispresentedwithfrequentlyrecurrentpainintheupperabdomenorstomacharea,whichismainlycausedbyexogenouspathogen,improperdietorinternalinjuriesduetosevenemotions.All45caseswithepigastricpaincausedbyvariousfactorsweretreatedwithmainlyneedlingHegu(LI4)betweenNovember2010andNovember2012,andthereportisgivenasfollows.
简介:在LiCl-KCl-MgCl2-ZnCl2-CaCl2熔盐体系中,以钼为惰性电极,在温度为943K时,直接电解制备Mg-Zn-Li-Ca四元合金。循环伏安研究表明,在LiCl-KCl熔盐体系中,添加MgCl2、ZnCl2和CaCl2后,Li的析出电位明显正移。计时电位研究表明,当阴极电流密度等于或者更负于-1.55A/cm2时,Mg、Li/Zn和Ca能够实现四元沉积。X射线衍射研究表明,恒电流电解可以制备出由不同相组成的Mg-Zn-Li-Ca合金。采用金相显微镜和电子扫描显微镜对合金样品进行表征。能谱分析结果表明,Mg元素和Ca元素在合金中分布均匀,而Zn元素主要分布在基体的边缘。
简介:ProgressivedelaminationdrivenbyLi-iondiffusioninelasticdisk-likethinfilmelectrodesofLi-ionbatteriesismodeledbasedonthecohesivemodel.Axisymmetricdiffusionmodelisconsideredunderbothgalvanostaticandpotentiostaticoperations.Theeffectofedgediffusiononthedelaminationprocessisevaluated.Itisfoundthatthediffusionfromedgeleadstoanearlierdelaminationinitiation.Theedgeeffectissignificantforactivediskswithasmallaspectratio,butnegligibleforthecaseoflargeaspectratio.Theedgediffusionisweakerinthepotentiostaticoperationthaninthegalvanostaticoperation.
简介:采用光学显微镜(OM)、扫描电镜(SEM)、能谱分析(EDX)和差示扫描热分析法(DSC)研究Al-Cu-Li-Mn-Zr-Ti合金在均匀化过程中的组织转变。结果表明,实验合金的铸态组织中存在严重的枝晶偏析,晶界处存在大量的共晶相,主要合金元素沿枝晶区域呈周期性分布。合金中的主要未溶相为Al2Cu相,过烧温度为520°C;均匀化过程中,随着温度的升高和时间的延长,晶界处的第二相逐渐溶入基体中,晶界逐渐变得稀疏;合金的均匀化过程可以用一指数方程描述;实验合金适宜的均匀化制度为(510°C,18h),这与采用均匀化动力学方程计算的结果基本吻合。
简介:通过固相法和溶胶-凝胶法合成不同碳含量的磷酸钒锂/C正极材料,研究了作为碳源的蔗糖和柠檬酸添加量对产物电化学性能的影响.实验发现,在固相合成方法中,添加量高于10.5%(质量百分数)时进一步增加蔗糖添加量后产物放电容量变化不明显.但是在溶胶-凝胶合成方法中,柠檬酸的添加量存在最佳值,高于或者低于此最佳数值都会引起产物容量的降低,这是与固相合成技术的一个明显不同之处.另一点不同之处在于对于溶胶凝胶合成的样品,最佳添加量与产物的工作电流有关.本实验条件下,在0.2C倍率以下柠檬酸与氢氧化锂最佳比值为1∶3,但是在放电倍率高于0.5C时最佳比值为1∶2.
简介:MesoporousLiFePO4/Ccompositescontaining80wt%ofhighlydispersedLiFePO4nanoparticles(4-6nm)werefabricatedusingbimodalmesoporouscarbon(BMC)ascontinuousconductivenetworks.TheuniqueporestructureofBMCnotonlypromisesgoodparticleconnectivityforLiFePO4,butalsoactsasarigidnano-confinementsupportthatcontrolstheparticlesize.Furthermore,thecapacitieswereinvestigatedrespectivelybasedontheweightofLiFePO4andthewholecomposite.Whencalculatedbasedontheweightofthewholecomposite,itis120mAh·g-1at0.1Cofthehighloadingelectrodeand42mAh·g-1at10Cofthelowloadingelectrode.TheelectrochemicalperformanceshowsthathighLiFePO4loadingbenefitslargetapdensityandcontributestotheenergystorageatlowrates,whiletheelectrodewithlowcontentofLiFePO4displayssuperiorhighrateperformance,whichcanmainlybeduetothesmallparticlesize,gooddispersionandhighutilizationoftheactivematerial,thusleadingtoafastionandelectrondiffusion.