Much demanded and overused are the critical rare-earth elements such as Pr, Nd, Dy, and Tb with increasing need of Nd Fe B-type rare-earth permanent magnets in the enlarging application areas, developing new high-tech...Much demanded and overused are the critical rare-earth elements such as Pr, Nd, Dy, and Tb with increasing need of Nd Fe B-type rare-earth permanent magnets in the enlarging application areas, developing new high-tech industries, and emerging cutting-age frontiers. The balance and efficient use of rare-earth resources comes into being the national strategy, national defense, and border safety for many major countries and regions in the world.（Nd,Ce）Fe B-based permanent magnetic materials, which can not only reduce cost but also offer a feasible way for integrated and effective utilization of rare earth resources,have received much attention in recent years. The existence of CeFe2 and the mixed valence state of Ce in Ce Fe B compound, the different metallurgy behavior and the particular processing as well as potential various magnetic-hardening mechanisms, however, make it quite different from Nd-based alloys.For instance, the coercivity of Ce-containing magnets in some certain composition range, is even higher than that of the counterpart pure Nd-based magnets though the Ce-containing magnets possess inferior intrinsic properties. Consequently, it is very important to design proper composition and structure, optimize processing, and analyze the mechanisms in depth for this kind of magnet. High performance and cost-effective magnets can be fabricated if we can make full use of the composition＇s inhomogeneous and abnormal coercivity variation of the Ce-containing permanent magnets. In this paper, we have summarized the phase structures, magnetic properties and microstructures of（Nd,Ce）Fe B-based permanent magnetic materials to shed light on further research and development of this type of so-called ＂gap magnet＂.展开更多
This review summarizes the recent advances on the application of ^(57)Fe Mössbauer spectrometry to study the magnetic and phase characteristics of Nd–Fe–B-based permanent magnets. First of all, the hyperfine st...This review summarizes the recent advances on the application of ^(57)Fe Mössbauer spectrometry to study the magnetic and phase characteristics of Nd–Fe–B-based permanent magnets. First of all, the hyperfine structures of the Ce_(2)Fe_(14)B,(Ce,Nd)_(2)Fe_(14)B and MM_(2)Fe_(14)B phases are well-defined by using the model based on the Wigner-Seitz analysis of the crystal structure. The results show that the isomer shift δ and the quadrupole splitting öEQ of those 2:14:1 phases show minor changes with the Nd content, while the hyperfine field Bhfincreases monotonically with increasing Nd content and its value is influenced by the element segregation and phase separation in the 2:14:1 phase. Then, the hyperfine structures of the low fraction secondary phases are determined by the ^(57)Fe Mössbauer spectrometry due to its high sensitivity. On this basis,the content, magnetic behavior, and magnetization of the REFe_(2) phase, the amorphous grain boundary(GB) phase, and the amorphous worm-like phase, as well as their effects on the magnetic properties, are systematically studied.展开更多
Objective:To classify 21 new isolates of Trypanosoma cruai(T.cruzi) according to the Discrete Typing Unit(DTU) which they belong to,as well as tune up a new pair of primers designed to detect the parasite in biologica...Objective:To classify 21 new isolates of Trypanosoma cruai(T.cruzi) according to the Discrete Typing Unit(DTU) which they belong to,as well as tune up a new pair of primers designed to detect the parasite in biological samples.Methods:Strains were isolated,DNA extracted,and classified by using three Polymerase Chain Reactions(PCR).Subsequently this DNA was used along with other isolates of various biological samples,for a new PCR using primers designed.Finally,the amplified fragments were sequenced.Results:It was observed the predominance of DTU i in Colombia,as well as the specificity of our primers for detection of T.cruzi,while no band was obtained when other species were used.Conclusions:This work reveals the genetic variability of 21 new isolates of T.cruzi in Colombia.Our primers confirmed their specificity for detecting the presence of T.cruzi.展开更多
Room-temperature electrocatalytic nitrogen reduction reaction(NRR)is of paramount significance for the fertilizer industry and fundamental catalysis science.However,many NRR catalysts were based on the use of metals.H...Room-temperature electrocatalytic nitrogen reduction reaction(NRR)is of paramount significance for the fertilizer industry and fundamental catalysis science.However,many NRR catalysts were based on the use of metals.Herein,we focus on exploring boron-based,metal-free,efficient catalysts for NRR by den-sity functional theory calculations with van der Waals corrections(DFT+D3).Our results show that the NRR performance of the boron active site can be improved by tuning the N-coordination environment in a graphene sheet,and the B-N-C structures show excellent stability.By considering the correlation be-tween the Bader charges of the boron dopant over N-decorated graphene and their NRR activities,the ra-tional design principle of a boron-based catalyst for NRR is developed.The boron-site with one pyridinic nitrogen in a double-vacancy structure is found to be a highly active center,with low reaction energy(0.53 eV)and kinetic barrier(0.84 eV)through the distal mechanism.We also found that the charge loss of boron considerably hampers hydrogen adsorption,which in turn promotes the NRR efficiency by hin-dering the competing hydrogen evolution.This work offers new insights into developing low-cost,highly effective boron-based materials as promising electrocatalysts for green ammonia synthesis.展开更多
This paper presents a basis for the space of hyperbolic polynomials Гm=span { 1, sht, cht, sh2t, ch2t shmt, chmt} on the interval [0,a] from an extended Tchebyshev system, which is analogous to the Bernstein basis fo...This paper presents a basis for the space of hyperbolic polynomials Гm=span { 1, sht, cht, sh2t, ch2t shmt, chmt} on the interval [0,a] from an extended Tchebyshev system, which is analogous to the Bernstein basis for the space of polynomial used as a kind of well-known tool for free-form curves and surfaces in Computer Aided Geometry Design. Then from this basis, we construct quasi Bézier curves and discuss some of their properties. At last, we give an example and extend the range of the parameter variable t to arbitrary close interval [r, s] （r〈s）.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 51564037 and 51661011)the Innovation Fund Designated for Graduate Students of Jiangxi Province (Grant No. YC2016-B078)the Qing Jiang Scholar and the Start-up Fund of Jiangxi University of Science and Technology (Grant No. 3208600001)
文摘Much demanded and overused are the critical rare-earth elements such as Pr, Nd, Dy, and Tb with increasing need of Nd Fe B-type rare-earth permanent magnets in the enlarging application areas, developing new high-tech industries, and emerging cutting-age frontiers. The balance and efficient use of rare-earth resources comes into being the national strategy, national defense, and border safety for many major countries and regions in the world.（Nd,Ce）Fe B-based permanent magnetic materials, which can not only reduce cost but also offer a feasible way for integrated and effective utilization of rare earth resources,have received much attention in recent years. The existence of CeFe2 and the mixed valence state of Ce in Ce Fe B compound, the different metallurgy behavior and the particular processing as well as potential various magnetic-hardening mechanisms, however, make it quite different from Nd-based alloys.For instance, the coercivity of Ce-containing magnets in some certain composition range, is even higher than that of the counterpart pure Nd-based magnets though the Ce-containing magnets possess inferior intrinsic properties. Consequently, it is very important to design proper composition and structure, optimize processing, and analyze the mechanisms in depth for this kind of magnet. High performance and cost-effective magnets can be fabricated if we can make full use of the composition＇s inhomogeneous and abnormal coercivity variation of the Ce-containing permanent magnets. In this paper, we have summarized the phase structures, magnetic properties and microstructures of（Nd,Ce）Fe B-based permanent magnetic materials to shed light on further research and development of this type of so-called ＂gap magnet＂.
基金Project supported by the Zhejiang Provincial Natural Science Foundation of China(Grant Nos.LY20E010002,LR18E010001,and LD19E010001)the National Natural Science Foundation of China(Grant Nos.U1704253 and 51801047)+2 种基金Liaoning Revitalization Talents Program(Grant No.XLYC1807177)the Key Research and Development plan of Zhejiang Province,China(Grant No.2020C05014)Ten Thousand Talents Plan of Zhejiang Province,China(Grant No.2018R52003)。
文摘This review summarizes the recent advances on the application of ^(57)Fe Mössbauer spectrometry to study the magnetic and phase characteristics of Nd–Fe–B-based permanent magnets. First of all, the hyperfine structures of the Ce_(2)Fe_(14)B,(Ce,Nd)_(2)Fe_(14)B and MM_(2)Fe_(14)B phases are well-defined by using the model based on the Wigner-Seitz analysis of the crystal structure. The results show that the isomer shift δ and the quadrupole splitting öEQ of those 2:14:1 phases show minor changes with the Nd content, while the hyperfine field Bhfincreases monotonically with increasing Nd content and its value is influenced by the element segregation and phase separation in the 2:14:1 phase. Then, the hyperfine structures of the low fraction secondary phases are determined by the ^(57)Fe Mössbauer spectrometry due to its high sensitivity. On this basis,the content, magnetic behavior, and magnetization of the REFe_(2) phase, the amorphous grain boundary(GB) phase, and the amorphous worm-like phase, as well as their effects on the magnetic properties, are systematically studied.
基金funded by a FPU a grant from the Ministry of Education of Spain
文摘Objective:To classify 21 new isolates of Trypanosoma cruai(T.cruzi) according to the Discrete Typing Unit(DTU) which they belong to,as well as tune up a new pair of primers designed to detect the parasite in biological samples.Methods:Strains were isolated,DNA extracted,and classified by using three Polymerase Chain Reactions(PCR).Subsequently this DNA was used along with other isolates of various biological samples,for a new PCR using primers designed.Finally,the amplified fragments were sequenced.Results:It was observed the predominance of DTU i in Colombia,as well as the specificity of our primers for detection of T.cruzi,while no band was obtained when other species were used.Conclusions:This work reveals the genetic variability of 21 new isolates of T.cruzi in Colombia.Our primers confirmed their specificity for detecting the presence of T.cruzi.
基金H.L.acknowledges the Center for Computational Materials Sci-ence,Institute for Materials Research,Tohoku University for the use of MASAMUNE-IMR(No.202212-SCKXX-0204)the In-stitute for Solid State Physics(ISSP)at the University of Tokyo for the use of their supercomputers+2 种基金the China BaoWu Low Carbon Metallurgical Innovation Foundation(No.BWLCF202113)the Fundamental Research Funds for the Cen-tral Universities(No.N2202012),JSPS KAKENHI(No.JP23K13703)the Iwatani Naoji Foundation.The authors thank the Beijing PARATERA Tech Co.,Ltd.for providing HPC resources.
文摘Room-temperature electrocatalytic nitrogen reduction reaction(NRR)is of paramount significance for the fertilizer industry and fundamental catalysis science.However,many NRR catalysts were based on the use of metals.Herein,we focus on exploring boron-based,metal-free,efficient catalysts for NRR by den-sity functional theory calculations with van der Waals corrections(DFT+D3).Our results show that the NRR performance of the boron active site can be improved by tuning the N-coordination environment in a graphene sheet,and the B-N-C structures show excellent stability.By considering the correlation be-tween the Bader charges of the boron dopant over N-decorated graphene and their NRR activities,the ra-tional design principle of a boron-based catalyst for NRR is developed.The boron-site with one pyridinic nitrogen in a double-vacancy structure is found to be a highly active center,with low reaction energy(0.53 eV)and kinetic barrier(0.84 eV)through the distal mechanism.We also found that the charge loss of boron considerably hampers hydrogen adsorption,which in turn promotes the NRR efficiency by hin-dering the competing hydrogen evolution.This work offers new insights into developing low-cost,highly effective boron-based materials as promising electrocatalysts for green ammonia synthesis.
基金Project supported by the National Natural Science Foundation of China (No. 60473130) and the National Basic Research Program (973) of China (No. 2004CB318000)
文摘This paper presents a basis for the space of hyperbolic polynomials Гm=span { 1, sht, cht, sh2t, ch2t shmt, chmt} on the interval [0,a] from an extended Tchebyshev system, which is analogous to the Bernstein basis for the space of polynomial used as a kind of well-known tool for free-form curves and surfaces in Computer Aided Geometry Design. Then from this basis, we construct quasi Bézier curves and discuss some of their properties. At last, we give an example and extend the range of the parameter variable t to arbitrary close interval [r, s] （r〈s）.
