The microstructures of B2-ordered NiA1 containing α-Fe precipitates have been investigated in terms of transmission electron microscopy. Fine precipitation of α-Fe (bcc structure) occurs in NiA1 by aging around 973...The microstructures of B2-ordered NiA1 containing α-Fe precipitates have been investigated in terms of transmission electron microscopy. Fine precipitation of α-Fe (bcc structure) occurs in NiA1 by aging around 973K. The aging behavior was investigated by microhandness measurements and the temperature dependence of the yield strength of precipitate- comaining B2- ordered NiA1 was investigated by compression tests over the temperature range of 673-1273K. The fine precipitation of α-Fe was found to enhance greatly the low and intermediate temperature yield strength. When the deformation temperature is over 1073K, the strength of precipitate- containing NiA1 was comparable to ternary solid solution hardening NiA1-Fe. Dislocations bypass the particles during deformation and typical Orowan loops were observed surrounding the or-Fe particles after deformation.展开更多
Nitric oxide(NO)is a crucial signaling molecule that regulates a wide range of metabolic pathways in different strata of organisms.In plants,nitrate reductase(NR)is a key enzyme for NO biosynthesis.There are two NR-en...Nitric oxide(NO)is a crucial signaling molecule that regulates a wide range of metabolic pathways in different strata of organisms.In plants,nitrate reductase(NR)is a key enzyme for NO biosynthesis.There are two NR-encoding genes in Arabidopsis genome,NIA1 and NIA2,which are precisely regulated and expressed in a tissue-specific manner.In this study,we found that the natural antisense transcript as-NIA1,transcribed from the 30 UTR of NIA1,stabilizes NIA1 mRNA to maintain its circadian oscillation in plants grown under the light/dark cycle.Importantly,as-NIA1-dependent NIA1 mRNA stability is indispensable for NIA1-mediated NO biosynthesis in guard cells and natural stomatal closure.Moreover,we revealed that polypyrimidine tract-binding 3(PTB3)regulates the stabilization of NIA1 mRNA by directly binding to UC-rich elements of as-NIA1.We further found that MTA deposits N^(6)-methyladenosine(m6 A)on as-NIA1,facilitating the as-NIA1-PTB3 interaction in vivo,in agreement with RNA structure prediction in that m6 Amediated structural alterations expose the UC-rich elements to enhance the accessibility of PTB3.Taken together,these findings reveal a novel molecular mechanism by which plants precisely manipulate NO biosynthesis to modulate light/dark-regulated stomatal movement,highlighting the coupling of RNA epigenetic modifications and structures shaping RNA-protein interactions in the regulation of hormone biosynthesis.展开更多
To investigate the origin of the strong dependence of martensitic transformation temperature on composition, the elastic properties of high temperature B2 phases of both NiTi and NiAI were calculated by a first-princi...To investigate the origin of the strong dependence of martensitic transformation temperature on composition, the elastic properties of high temperature B2 phases of both NiTi and NiAI were calculated by a first-principle method, the exact-muffin orbital method within coherent potential approximation. In the composition range of 50-56 at. pct Ni of NiTi and 60-70 at. pct Ni of NiAI in which martensitic transformation occurs, non-basalplane shear modulus c44 increases with increasing Ni content, while basal-plane shear modulus c＇ decreases. In the above composition ranges however the transformation temperature of NiAI increases with increasing Ni content while that of NiTi decreases from experimental observation. The softening of c＇ is experimentally observed only in NiAI, and the decrease of c＇ with increasing Ni content is responsible for the increase of transformation temperature. The result of the present work demonstrates that, besides c＇, c44 also influences the martensitic transformation of NiTi and plays quite important a role.展开更多
The microstructure, high strain rate superplasticity and tensile creep behavior of directionally solidified （DS） NiAI-Mo（Hf） alloy have been investigated. The alloy exhibits dendritic structure, where dendritic ar...The microstructure, high strain rate superplasticity and tensile creep behavior of directionally solidified （DS） NiAI-Mo（Hf） alloy have been investigated. The alloy exhibits dendritic structure, where dendritic arm is NiAI phase, interdendritic region is Ni3AI phase, and Mo-rich phase distributes in the NiAI and Ni3AI phases. The alloy exhibits high strain rate superplastic deformation behavior, and the maximum elongation is 104.2% at 1373 K and strain rate of 1.04xi0-2 s-I. The balance between strain hardening （by dislocation glide） and strain softening （by dynamic recovery and recrystallization） is responsible for the superplastic deformation. All the creep curves of the DS NiAI-Mo（Hf） alloy have similar shape of a short primary creep and dominant steady creep stages, and the creep strain is great. The possible creep deformation mechanism was also discussed. The creep fracture data follow the Monkman-Grant relationship.展开更多
文摘The microstructures of B2-ordered NiA1 containing α-Fe precipitates have been investigated in terms of transmission electron microscopy. Fine precipitation of α-Fe (bcc structure) occurs in NiA1 by aging around 973K. The aging behavior was investigated by microhandness measurements and the temperature dependence of the yield strength of precipitate- comaining B2- ordered NiA1 was investigated by compression tests over the temperature range of 673-1273K. The fine precipitation of α-Fe was found to enhance greatly the low and intermediate temperature yield strength. When the deformation temperature is over 1073K, the strength of precipitate- containing NiA1 was comparable to ternary solid solution hardening NiA1-Fe. Dislocations bypass the particles during deformation and typical Orowan loops were observed surrounding the or-Fe particles after deformation.
基金funded by the National Key R&D Program of China 2022YFD1400800the National Science Foundation of China,China(no.32170293).
文摘Nitric oxide(NO)is a crucial signaling molecule that regulates a wide range of metabolic pathways in different strata of organisms.In plants,nitrate reductase(NR)is a key enzyme for NO biosynthesis.There are two NR-encoding genes in Arabidopsis genome,NIA1 and NIA2,which are precisely regulated and expressed in a tissue-specific manner.In this study,we found that the natural antisense transcript as-NIA1,transcribed from the 30 UTR of NIA1,stabilizes NIA1 mRNA to maintain its circadian oscillation in plants grown under the light/dark cycle.Importantly,as-NIA1-dependent NIA1 mRNA stability is indispensable for NIA1-mediated NO biosynthesis in guard cells and natural stomatal closure.Moreover,we revealed that polypyrimidine tract-binding 3(PTB3)regulates the stabilization of NIA1 mRNA by directly binding to UC-rich elements of as-NIA1.We further found that MTA deposits N^(6)-methyladenosine(m6 A)on as-NIA1,facilitating the as-NIA1-PTB3 interaction in vivo,in agreement with RNA structure prediction in that m6 Amediated structural alterations expose the UC-rich elements to enhance the accessibility of PTB3.Taken together,these findings reveal a novel molecular mechanism by which plants precisely manipulate NO biosynthesis to modulate light/dark-regulated stomatal movement,highlighting the coupling of RNA epigenetic modifications and structures shaping RNA-protein interactions in the regulation of hormone biosynthesis.
基金Part of the calculations in this work was performed ona Shenteng 6800 supercomputer at CNIC, China.
文摘To investigate the origin of the strong dependence of martensitic transformation temperature on composition, the elastic properties of high temperature B2 phases of both NiTi and NiAI were calculated by a first-principle method, the exact-muffin orbital method within coherent potential approximation. In the composition range of 50-56 at. pct Ni of NiTi and 60-70 at. pct Ni of NiAI in which martensitic transformation occurs, non-basalplane shear modulus c44 increases with increasing Ni content, while basal-plane shear modulus c＇ decreases. In the above composition ranges however the transformation temperature of NiAI increases with increasing Ni content while that of NiTi decreases from experimental observation. The softening of c＇ is experimentally observed only in NiAI, and the decrease of c＇ with increasing Ni content is responsible for the increase of transformation temperature. The result of the present work demonstrates that, besides c＇, c44 also influences the martensitic transformation of NiTi and plays quite important a role.
基金supported by the Dr.Start Fund of Liaoning Science and Technology Agency(No. 20021071)the Program of the Innovation Team of Liaoning Office of Education (No. 2006T078)
文摘The microstructure, high strain rate superplasticity and tensile creep behavior of directionally solidified （DS） NiAI-Mo（Hf） alloy have been investigated. The alloy exhibits dendritic structure, where dendritic arm is NiAI phase, interdendritic region is Ni3AI phase, and Mo-rich phase distributes in the NiAI and Ni3AI phases. The alloy exhibits high strain rate superplastic deformation behavior, and the maximum elongation is 104.2% at 1373 K and strain rate of 1.04xi0-2 s-I. The balance between strain hardening （by dislocation glide） and strain softening （by dynamic recovery and recrystallization） is responsible for the superplastic deformation. All the creep curves of the DS NiAI-Mo（Hf） alloy have similar shape of a short primary creep and dominant steady creep stages, and the creep strain is great. The possible creep deformation mechanism was also discussed. The creep fracture data follow the Monkman-Grant relationship.
