The incorporation of the quasicrystalline phase into the metal matrix offers a wide range of potential applications in particle-reinforced metal-matrix composites.The analytic solution of the piezoelectric quasicrysta...The incorporation of the quasicrystalline phase into the metal matrix offers a wide range of potential applications in particle-reinforced metal-matrix composites.The analytic solution of the piezoelectric quasicrystal(QC)microsphere considering the thermoelectric effect and surface effect contained in the elastic matrix is presented in this study.The governing equations for the QC microsphere in the matrix subject to the external electric loading are derived based on the nonlocal elastic theory,electro-elastic interface theory,and eigenvalue method.A comparison between the existing results and the finite-element simulation validates the present approach.Numerical examples reveal the effects of temperature variation,nonlocal parameters,surface properties,elastic coefficients,and phason coefficients on the phonon,phason,and electric fields.The results indicate that the QC microsphere enhances the mechanical properties of the matrix.The results are useful for the design and understanding of the characterization of QCs in micro-structures.展开更多
氮素是植物生长发育所需的大量元素之一,施用氮肥是农业生产中提高农作物产量的重要手段。自20世纪60年代以来,“绿色革命”半矮秆农作物品种的育成和大面积推广有效地解决了“高产与倒伏”之间的矛盾,提高了农作物的收获指数和产量。...氮素是植物生长发育所需的大量元素之一,施用氮肥是农业生产中提高农作物产量的重要手段。自20世纪60年代以来,“绿色革命”半矮秆农作物品种的育成和大面积推广有效地解决了“高产与倒伏”之间的矛盾,提高了农作物的收获指数和产量。然而半矮秆水稻和小麦品种也表现出生长发育对氮肥响应减弱、根系对铵态氮和硝态氮的吸收能力下降以及氮肥利用效率(nitrogen use efficiency,NUE)低的弊病,其产量增加依赖于氮肥的大量投入,这不仅提高了种植成本还导致了严重的环境污染问题。因此,提高农作物氮肥利用效率对于保障国家粮食安全和农业可持续发展具有重要战略意义。本文概述了“绿色革命”与赤霉素的作用机理,系统总结了植物氮素吸收、同化和代谢调控方面的研究进展,并介绍了提高作物氮肥利用效率的最新研究发现,以期为作物氮肥高效利用的遗传改良提供参考。展开更多
Dear Editor,Dispute between agriculture and initial population expansion in Neolithic Time has been in suspense for a long time.Agriculture first appeared in the Fertile Crescent of West Asia about 11–12 thousand yea...Dear Editor,Dispute between agriculture and initial population expansion in Neolithic Time has been in suspense for a long time.Agriculture first appeared in the Fertile Crescent of West Asia about 11–12 thousand years ago(kya),with domesticating few wild plant and animal species.There is also evidence of the cultivation of rice and millet in Yangtze and Yellow River Basins of China approximately 9 kya.During the subsequent times between 9 and 4 kya,agriculture展开更多
基金supported by the National Natural Science Foundation of China(Nos.U2067220 and 82000980)。
文摘The incorporation of the quasicrystalline phase into the metal matrix offers a wide range of potential applications in particle-reinforced metal-matrix composites.The analytic solution of the piezoelectric quasicrystal(QC)microsphere considering the thermoelectric effect and surface effect contained in the elastic matrix is presented in this study.The governing equations for the QC microsphere in the matrix subject to the external electric loading are derived based on the nonlocal elastic theory,electro-elastic interface theory,and eigenvalue method.A comparison between the existing results and the finite-element simulation validates the present approach.Numerical examples reveal the effects of temperature variation,nonlocal parameters,surface properties,elastic coefficients,and phason coefficients on the phonon,phason,and electric fields.The results indicate that the QC microsphere enhances the mechanical properties of the matrix.The results are useful for the design and understanding of the characterization of QCs in micro-structures.
文摘氮素是植物生长发育所需的大量元素之一,施用氮肥是农业生产中提高农作物产量的重要手段。自20世纪60年代以来,“绿色革命”半矮秆农作物品种的育成和大面积推广有效地解决了“高产与倒伏”之间的矛盾,提高了农作物的收获指数和产量。然而半矮秆水稻和小麦品种也表现出生长发育对氮肥响应减弱、根系对铵态氮和硝态氮的吸收能力下降以及氮肥利用效率(nitrogen use efficiency,NUE)低的弊病,其产量增加依赖于氮肥的大量投入,这不仅提高了种植成本还导致了严重的环境污染问题。因此,提高农作物氮肥利用效率对于保障国家粮食安全和农业可持续发展具有重要战略意义。本文概述了“绿色革命”与赤霉素的作用机理,系统总结了植物氮素吸收、同化和代谢调控方面的研究进展,并介绍了提高作物氮肥利用效率的最新研究发现,以期为作物氮肥高效利用的遗传改良提供参考。
基金supported by the National Excellent Youth Science Foundation of China (31222030)National Natural Science Foundation of China (91131002)+1 种基金MOE Scientific Research Project (113022A)Shanghai Shuguang Project (14SG05).
文摘Dear Editor,Dispute between agriculture and initial population expansion in Neolithic Time has been in suspense for a long time.Agriculture first appeared in the Fertile Crescent of West Asia about 11–12 thousand years ago(kya),with domesticating few wild plant and animal species.There is also evidence of the cultivation of rice and millet in Yangtze and Yellow River Basins of China approximately 9 kya.During the subsequent times between 9 and 4 kya,agriculture
