简介:Manybiologicalmaterials,suchaswoodandbone,possesshelicoidmicrostructuresatmicroscale,whichcanserveasreinforcingelementstotransferstressbetweencracksurfacesandimprovethefracturetoughnessoftheircomposites.Failureprocesses,suchasfiber/matrixinterfacedebondingandslidingassociatedwithpull-outofhelicalfibers,areresponsiblemainlyforthehighenergydissipationneededforthefracturetoughnessenhancement.Herewepresentsystemicanalysesofthepull-outbehaviorofahelicalfiberfromanelasticmatrixviathefiniteelementmethod(FEM)simulation,withimplicationsregardingtheunderlyingtougheningmechanismofhelicoidmicrostructures.Wefindthat,throughtheiruniformcurvatureandtorsion,helicalfiberscanprovidehighpull-outforceandlargeinterfaceareas,resultinginhighenergydissipationthataccounts,toalargeextent,forthehightoughnessofbiologicalmaterials.Thehelicityoffibershapeintermsofthehelicalanglehassignificanteffectsontheforce-displacementrelationshipsaswellasthecorrespondingenergydissipationduringfiberpull-out.
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简介:Atpresent,asWesterneconomiesslowdowninasynchronizedmanner,emergingeconomiesarealsobeingconfrontedwithdifficulties.ThedirectionoftheworldeconomywillprimarilybedeterminedbywhethertheU.S."fiscalcliff"canbeaddressedsmoothlyandwhetherthesovereigntydebtcrisiscanbeeffectivelycontrolledintheshort-term.Inthelong-termthedirectionoftheworldeconomywilldependonwhetheranewtechnologicalrevolutionwillmakebreakthroughachievements.
简介:Down综合征(DS),译为唐氏综合征,其临床表现典型,主要为智力发育迟缓、张力低下、小头畸形、宽眼距、低鼻梁、四肢短小、通贯掌、伸舌及吊眼稍(眼角上斜)等,是智力低下最常见的原因,又名先天愚型.其发病率随人种和地区有差异,约为1/1000~1/600.我国近年由于计划生育政策的实施,高龄产妇减少,发病率由50~70年代的1.3‰降至近十余年的0.7‰[1].DS的发病原因是患者细胞内多一条21号染色体.已知21染色体长臂二区二带是引起异常表型的决定性部位.此外有作者提出此病可能与放射线及化学物质等致畸变物质有关.
简介:Inthenewera,thepushandpullfactorsinChina-U.S.cooperationareemerginganddevelopingcenteringonwhethertheycouldreadjusttherelationshipbetweentherisingpowerandtheestablishedpowerinastablemanner.Therefore,China-U.S.cooperationshouldgraduallyresolvethestructuralconflictsinnecessarystrugglesandconsultations.Andtheall-aroundcooperationshouldbeplannedandpromotedintheaspectslike