简介：ExaminingChina'spopulationchangesinthepastthreedecadesdemonstratesthatChina'sdemographictransitionhasbeensuccessfullycompletedwithasplendidandzigzagpath.Thereareprofoundhistoricalexperiencesandlessons.ThispaperreviewsChina'sfertilitytransitionwhichisdividedintofourperiodsandarguesthatfertilitychangesarearesultoftheinteractionsbetweensocioeconomicdevelopment,fertilitybehaviorsandfertilitypolicies.Substantialresistancetothe'one-childpolicy'during1979to1984resultedinreboundingandfluctuatingfertility.Thebabyboomoccurredintheperiod1985to1991wasamanifestationoftheinherentlawsofdemographicdynamics,andsubsequentlyforcefulbirthcontrolwasagainmobilized.Theperiodfrom1992to1999witnessedlargedeclinesinfertilitywhichpenetratesthereplacementzone,showingthatChinawascompletingthefertilitytransition.China'sstabilizinglowfertilityandemergingpopulationstructuralissuessince2000callforcomprehensivewaysinaddressingthepopulationproblems.

简介：Theadiabaticelectrontransportistheoreticallystudiedinazigzaggraphenenanoribbon(ZGNR)junctionwithtwotime-dependentpumpingelectricfields.BymodelingaZGNRp–njunctionandapplyingtheKeldyshGreen’sfunctionmethod,wefindthatapumpedchargecurrentisflowinginthedeviceatazeroexternalbias,whichmainlycomesfromthephoton-assistedtunnelingprocessandthevalleyselectionruleinaneven-chainZGNRjunction.ThepumpedchargecurrentanditsONandOFFstatescanbeefficientlymodulatedbychangingthesystemparameterssuchasthepumpingfrequency,thepumpingphasedifference,andtheFermilevel.AferromagneticZGNRdeviceisalsostudiedtogenerateapurespincurrentandafullypolarizedspincurrentduetothecombinedspinpumpeffectandthevalleyvalveeffect.Ourfindingmightpavethewaytomanipulatethedegreeoffreedomofelectronsinagraphene-basedelectronicdevice.

简介：Theelectricfieldeffectinultrathinzigzaggraphenenanoribbonscontainingonlythreeorfourzigzagcarbonchainsisstudiedbyfirst-principlescalculations,andthechangeofconductingmechanismisobservedwithincreasingin-planeelectricfieldperpendiculartotheribbon.Widerzigzaggraphenenanoribbonshavebeenpredictedtobespin-splittedforbothvalencebandmaximum(VBM)andconductionbandminimum(CBM)withanappliedelectricfieldandbecomehalf-metalduetothevanishingbandgapofonespinwithincreasingappliedfield.ThechangeofVBMfortheultrathinzigzaggraphenenanoribbonsissimilartothatforthewideroneswhenanelectricfieldisapplied.However,intheultrathinzigzaggraphenenanoribbons,therearetwokindsofCBMs,oneisspin-degenerateandtheotherisspin-splitted,andbotharetunablebytheelectricfield.Moreover,thetwoCBMsarespatiallyseparatedinmomentumspace.Theconductingmechanismchangesfromspin-degenerateCBMtospin-splittedCBMwithincreasingappliedelectricfield.OurresultsareconfirmedbydensityfunctionalcalculationswithbothLDAandGGAfunctionals,inwhichtheLDAalwaysunderestimatesthebandgapwhiletheGGAnormallyproducesabiggerbandgapthantheLDA.

简介：Ahigh-repetitionratemasteroscillatorpoweramplifierpumpedwithlaserdiodes(LDs)isreported.Aninjectionseedingsingle-frequencyelectro-opticalQ-switchedNd:YAGlaserisusedasanoscillator,andaconductivelycooledNd:YAGzigzagslabwithabounce-pumpedarchitectureisutilizedasapoweramplifier.Pulseenergiesofover800mJat1064nmand400mJat532nm,correspondingtoaveragepowersof200and100W,respectively,areachievedwitha12.6-nspulsewidthat250Hz.Outputfrequencyfluctuationsandsingle-frequencyoperationarefurthermonitored.Experimentalresultsrevealthattheproposedsystem,whichfeaturesasingle-passamplifiedconfiguration,isapromisingdesignforspace-basedapplications.

简介：运用转移矩阵的技巧,本文给出了戴帽B27N27硼-氮zlgzag纳米管的克库勒结构数的计算公式.在实际计算中,根据管的对称性,转移矩阵的阶得到了显著地降低.