It is an important way to realize rural revitalization and sustainable development to guide rural settlement transition(RST)in an appropriate way.This paper uses actor network theory(ANT)to construct a theoretical fra...It is an important way to realize rural revitalization and sustainable development to guide rural settlement transition(RST)in an appropriate way.This paper uses actor network theory(ANT)to construct a theoretical framework for the study of RST.Taking two typical villages with different transition paths in rural areas of North China Plain as examples,this paper reveals the mechanism of RST and makes a comparative analysis.The results show that:1)after identifying problems and obligatory passage point,key actors recruit heterogeneous actors into the actor network by entrusting them with common interests,and realize RST under the system operation.2)Rural settlements under different transition paths have similarities in the problems to be solved,collective actions and policy factors,but there are differences in the transition process,mechanism and effect.The actor network and mechanism of RST through the path of new rural community construction are more complex and the transition effect is more thorough.In contrast,the degree of RST of retention development path is limited if there is no resource and location advantage.3)Based on the applicable conditions of different paths,this paper designs a logical framework of‘Situation-Structure-Behavior-Result’to scientifically guide the identification of RST paths under the background of rural revitalization.展开更多
Energy development has a significant impact on urbanization. This study employs the entropy method to evaluate the level of urbanization in Central Asia and further analyzes the possible dynamic transition mechanisms ...Energy development has a significant impact on urbanization. This study employs the entropy method to evaluate the level of urbanization in Central Asia and further analyzes the possible dynamic transition mechanisms of the impact of energy development (characterized by energy development scale, energy trade, energy consumption, and energy endowment) on urbanization using the Panel Smooth Transition Regression model (PSTR). The results demonstrate that energy development in this region is characterized by “three highs and one low”, namely, high production volume, high export volume, high endowment, and low self-consumption, and plays a crucial role in the progress of urbanization. A nonlinear relationship is found to exist between energy development and comprehensive urbanization in the transition economies of Central Asia. Generally speaking, as energy development continues to expand, its impact on urbanization in this region has shifted from constraint to promotion, with the latter gradually tending to flatten out. Energy development characterized by energy development scale, energy consumption, and energy trade can prove the point, whose threshold is 1.47 million tons oil equivalent (Mtoe), 0.29 tons oil equivalent (toe) per capita, and 20.95 Mtoe, respectively. However, not all energy development models exhibit this behavior. Energy development characterized by energy endowment is such a case where the positive effect of it on comprehensive urbanization will be restrained when it exceeds 3.18. These findings can aid decision makers in seeking a better energy development model to promote the sustainable development of urbanization in Central Asia, avoiding energy resources waste and disorderly development.展开更多
IPv4 and IPv6 will coexist for many years during the transition period from the traditional IPv4-based Internet to an IPv6-based Internet.DHTLayer,a novel IPv4/IPv6 transition mechanism based on Distributed Hash Table...IPv4 and IPv6 will coexist for many years during the transition period from the traditional IPv4-based Internet to an IPv6-based Internet.DHTLayer,a novel IPv4/IPv6 transition mechanism based on Distributed Hash Table(DHT) is presented in this paper.It can fully support IPv4 and IPv6 inter-operation.DHTLayer employs a DHT overlay to maintain the routing information between IPv4 and IPv6.It decouples path selection from packet delivery.In DHTLayer,the Looking-Up Route Path is responsible for selecting paths,and then the Delivering Process takes charge of delivering IP packets along the path selected above.Simulation results show that it is very effective and efficient.展开更多
This paper studied the active-to-passive oxidative mechanism of C/SiC composite under high temperature and oxidative conditions. An analytic model and computational method were established based on the process of gas ...This paper studied the active-to-passive oxidative mechanism of C/SiC composite under high temperature and oxidative conditions. An analytic model and computational method were established based on the process of gas diffusion in boundary layer and the equilibrium relations in surface chemical reactions. Simultaneously, an engineering equation to predict the oxygen partial pressure of active-to-passive transition was derived under the specific temperature zone. The results indicated that the active-to-passive oxidation transition of C/SiC is closely related to the composition of the material. At certain temperature and oxygen partial pressure conditions, the composite with high carbon content is prone to cause active oxidation which is negative to the oxidation resistance of the material.展开更多
Efficient capture,safe storage and release of tritium from the international thermonuclear experimental reactor(ITER) reaction exhaust gas is a perplexing problem,and the development of an efficient tritium-getter mat...Efficient capture,safe storage and release of tritium from the international thermonuclear experimental reactor(ITER) reaction exhaust gas is a perplexing problem,and the development of an efficient tritium-getter material with ultra-low hydrogenation equilibrium pressure is considered as a reliable way.In this work,Zr_(2)Co alloy was selected as a tritium-getter material and prepared through induction levitation melting.Fundamental performance test results show that Zr_(2)Co exhibits an ultra-low hydrogenation equilibrium pressure of 3.22 × 10^(-6) Pa at 25℃ and excellent hydriding kinetics under a low hydrogen pressure of 0.005 MPa.Interestingly,unique phase transition behaviors were presented in Zr_(2)Co-H system.Specifically,Zr_(2)CoH_(5) formed by Zr_(2)Co hydrogenated at room temperature is initially decomposed into ZrH_(2) and ZrCoH_(3) at200 ℃.With the temperature increasing to 350 ℃,ZrCoH_(3)is dehydrogenated to ZrCo,and then ZrCo further reacts with ZrH_(2) at 650 ℃ to reform Zr_(2)Co and hydrogen.Among the staged phase transition pathways during dehydrogenation,the decomposition of Zr_(2)CoH_(5) occurs preferentially,which is well accordance with both the smallest reaction energy barrier and the maximum reaction spontaneity that are determined respectively from kinetics activation energy and thermodynamics Gibbs free energy.Furthermore,first principles calculation results indicate that the stronger binding of hydrogen in interstitial environments of ZrCoH_(3)and ZrH_(2) triggers the hydrogen-stabilized phase transformation of Zr_(2)CoH_(5).The unique phase transition mechanisms in Zr_(2)Co-H system can shed light on the further exploration and regulation of analogous staged phase transition of hydrogen storage materials.展开更多
As an important kind of intelligent materials,shape-memory materials have been received increasing attention on account of their interesting properties and potential applications in recent years.Particularly,the rise ...As an important kind of intelligent materials,shape-memory materials have been received increasing attention on account of their interesting properties and potential applications in recent years.Particularly,the rise of shape-memory polymers by far surpasses well-known metallic shape-memory alloys in their shape-memory properties.The advantages of polymers compared to other materials are their easier availability and their wide range of mechanical and physical properties.The polymers designed to exhibit a shape-memory effect require two components on the molecular level:crosslinks to determine the permanent shape and switching segments with Ttrans to fix the temporary shape.Up to now almost all papers on shape-memory polymers introduce switching segments with the covalent linking method.On the other hand,only several cases concern non-covalent interaction.However,the research works mentioned above is based on a single Trans(i.e.,Tm or Tg).展开更多
Systemic measurements show that there is no 3D to 2D crossover in the reduction of the superconducting transition temperature Tc in Nb thin films. This result is consistent with all previous measurements while it is c...Systemic measurements show that there is no 3D to 2D crossover in the reduction of the superconducting transition temperature Tc in Nb thin films. This result is consistent with all previous measurements while it is contrary to the prevailing understanding based on the interplay between proximity, localization, and lifetime broadening. Our study indicates that the decrease of Tc can be interpreted by the combined effects of electron-phonon coupling parameter λ and the defect scattering rate pw, being uniquely determined by their ratio λ/ρw. Other factors such as film thickness and irradiation do not produce additional effects beyond these two parameters.展开更多
I am happy to attend this symposium at the invitation of the Tokyo Consortium. China and Japan are close neighbors, separated only bya narrow strip of sea. Exchanges have been frequent between the Chinese and Japanese...I am happy to attend this symposium at the invitation of the Tokyo Consortium. China and Japan are close neighbors, separated only bya narrow strip of sea. Exchanges have been frequent between the Chinese and Japanese peoples since ancient times. In striving for modernization,展开更多
Effects of hydrogen on the mechanical properties of differently aged 7175 aluminum alloys were investigated by using cathodic H-permeation, slow strain rate tension and so on. The results indicate that both the yield ...Effects of hydrogen on the mechanical properties of differently aged 7175 aluminum alloys were investigated by using cathodic H-permeation, slow strain rate tension and so on. The results indicate that both the yield stress and the percentage reduction of area decrease with increasing hydrogen charging time, and the degree of reduction decreases as aging time increases for the same hydrogen charging time.展开更多
The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys （Al86Ni8Y6, Al86GNi6Y6Co2, Al86NigLa6 and Al86Ni8Y45La15） synthesized via mechanical alloying by varying...The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys （Al86Ni8Y6, Al86GNi6Y6Co2, Al86NigLa6 and Al86Ni8Y45La15） synthesized via mechanical alloying by varying the composition, i.e. fully or partially replacing rare earth （RE） and transition metal （TM） elements based on similar atomic radii and coordination number. X-ray diffraction and high resolution transmission electron microscopy study revealed that the amorphization process occurred through formation of various intermetallic phases and nanocrystalline FCC Al. Fully amorphous phase was obtained for the alloys not containing lanthanum, whereas the other alloys containing La showed partial amorphization with reappearance of intermetallic phases attributed to mechanical crystallization. Differential scanning calorimetry study confirmed better thermal stability with wider transformation temperature for the alloys without La.展开更多
Lonsdaleite,also known as hexagonal diamond,is an allotrope of carbon with a hexagonal crystal structure,which was discovered in the nanostructure of the Canyon Diablo meteorite.Theoretical calculations have shown tha...Lonsdaleite,also known as hexagonal diamond,is an allotrope of carbon with a hexagonal crystal structure,which was discovered in the nanostructure of the Canyon Diablo meteorite.Theoretical calculations have shown that this structure gives it exceptional physical properties that exceed those of cubic diamond,making it highly promising for groundbreaking applications in superhard cutting tools,wide-bandgap semiconductor devices,and materials for extreme environments.As a result,the controllable synthesis of hexagonal diamond has emerged as a cutting-edge research focus in materials science.This review briefly outlines the progress in this area,with a focus on the mechanisms governing its key synthesis conditions,its intrinsic physical properties,and its potential applications in various fields.展开更多
Doping is critical for inducing ferroelectricity in hafnia films,yet the underlying mechanisms remain debated.Here,through first-principles studies,we elucidate the pivotal role played by the complex phase transition ...Doping is critical for inducing ferroelectricity in hafnia films,yet the underlying mechanisms remain debated.Here,through first-principles studies,we elucidate the pivotal role played by the complex phase transition mechanisms under carrier doping in understanding the origin of hafnia ferroelectricity.Specifically,electron doping orchestrates a metastable polar phase to stable antipolar phase transformation,driven by strong screening effects and weakened nonpolar covalent bonds,making n-type dopants rare.Conversely,weak screening effect and enhanced polar covalent bonding strengthen robust ferroelectricity,enabling significant ground-state phase transitions from the monoclinic to the polar orthorhombic phase and finally to the cubic phase under hole doping,a phenomenon prevalent in hafnia-based films doped with p-type dopants.Furthermore,this holeenhanced polar distortion also results in an inverse size effect in hafnia ferroelectric films,unlike perovskite ferroelectrics.Our findings offer new insights into the preparation of robust hafnia-based ferroelectric films through doping or interface engineering.展开更多
Nb has a positive effect on improving the mechanical properties of metal materials, and it is expected to strengthen CoCrCuFeNi high-entropy alloys （HEAs） with outstanding ductility and relatively weak strength. In ...Nb has a positive effect on improving the mechanical properties of metal materials, and it is expected to strengthen CoCrCuFeNi high-entropy alloys （HEAs） with outstanding ductility and relatively weak strength. In this paper, the alloying effects of Nb on the microstructural evolution and the mechanical properties of the （CoCrCuFeNi）100-xNbx HEA were investigated systematically. The result shows that Nb promotes the phase transition from FCC （face-centered cubic） to Laves phase, and the volume fractions of Laves phase increase from 0% to 58.2% as the Nb content increases, Compressive testing shows that the addition of Nb has a positive effect on improving the strength of CoCrCuFeNi HEA. The compressive yield strength of （CoCrCuFeNi）100-xNbx HEAs increases from 338 MPa to 1322 MPa and the fracture strain gradually reduces from 60.0% （no fracture） to 8.1% as the Nb content increases from 0 to 16 at.%. The volume fraction increase of hard Laves phase is the key factor for the strength increase, and the reduction of the VEC （valence electron concentration） value induced by the addition of Nb is beneficial for the increase of the Laves phase content in these alloys.展开更多
The feasibility of using coral reef sand（CRS） in Portland cement concrete is investigated by testing the mechanical property and microstructure of concrete. The composition, structure and properties of the CRS are a...The feasibility of using coral reef sand（CRS） in Portland cement concrete is investigated by testing the mechanical property and microstructure of concrete. The composition, structure and properties of the CRS are analyzed. Mechanical properties and microstructure of concrete with CRS are studied and compared to concrete with natural river sand. The relationship between the microstructure and performance of CRS concrete is established. The CRS has a porous surface with high water intake capacity, which contributes to the mechanical properties of concrete. The interfacial transition zone between the cement paste and CRS is densified compared to normal concrete with river sand. Hydration products form in the pore space of CRS and interlock with the matrix of cement paste, which increases the strength. The total porosity of concrete prepared with CRS is higher than that with natural sand. The main difference in pore size distribution is the fraction of fine pores in the range of 100 nm.展开更多
This paper extends the flux scattering method to study the carrier transport property in nanoscale MOSFETs with special emphasis on the low-field mobility and the transport mechanism transition. A unified analytical e...This paper extends the flux scattering method to study the carrier transport property in nanoscale MOSFETs with special emphasis on the low-field mobility and the transport mechanism transition. A unified analytical expression for the low-field mobility is proposed, which covers the entire regime from drift-diffusion transport to quasi-ballistic transport in 1-D, 2-D and 3-D MOSFETs. Two key parameters, namely the long-channel low-field mobility （λ0） and the low-field mean free path （λ0）, are obtained from the experimental data, and the transport mechanism transition in MOSFETs is further discussed both experimentally and theoretically. Our work shows that λ0 is available to characterize the inherent transition of the carrier transport mechanism rather than the low-field mobility. The mobility reduces in the MOSFET with the shrinking of the channel length; however, λ0 is nearly a constant, and λ0 can be used as the ＂entry criterion＂ to determine whether the device begins to operate under quasi-ballistic transport to some extent.展开更多
The cuticle of a maggot goes through a mechanical transition when it dries, increasing in stiffness by about an order of magnitude (e.g. from 0.5 GPa to 5 GPa) as the water content drops from about 1 g/g (weight of wa...The cuticle of a maggot goes through a mechanical transition when it dries, increasing in stiffness by about an order of magnitude (e.g. from 0.5 GPa to 5 GPa) as the water content drops from about 1 g/g (weight of water per unit dry weight) to 0.4 g/g. Thus stiffness represents the loss of freezable water and is more or less diagnostic of a material stabilized by hydrogen bonds. Further loss in water results in a smaller increase in stiffness. In natural systems the water content is controlled by the addition of phenolic residues, resulting in tanning or sclerotisation, which drives the matrix components towards co-operative interaction and makes the material permanently waterproof.展开更多
Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of rubidium metal hydrides RbMH4（M = B, Al, Ga） for five different crystal structures, nam...Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of rubidium metal hydrides RbMH4（M = B, Al, Ga） for five different crystal structures, namely hexagonal（P63mc）, tetragonal（P42/nmc）, tetragonal（P421c）, orthorhombic（Pnma） and monoclinic（P21/c）. Among the considered structures, tetragonal（P421c） phase is found to be the most stable one for these metal hydrides at normal pressure. A pressure-induced structural phase transition from tetragonal（P421c） to monoclinic（P21/c） phase is observed in all the three metal hydrides. The electronic structure reveals that these hydrides are wide band gap semiconductors. The calculated elastic constants indicate that these alkali metal tetrahydrides are mechanically stable at normal pressure.展开更多
We investigated mechanical properties of concretes made with impurity aggregates of different combinations. Besides the mechanisms were explored by EDS, CT, and hardness testing. The results showed that fully rust-sta...We investigated mechanical properties of concretes made with impurity aggregates of different combinations. Besides the mechanisms were explored by EDS, CT, and hardness testing. The results showed that fully rust-stained and surface rust-stained sandstone aggregate had significant adverse impact on the compressive strength of concrete while sandstone aggregate had a much more obvious impact on the ultimate tension of concrete. Concrete crack was more prone to expand along surfaces and the micro-hardness of interfacial transition zone of different aggregates was ranked in decreasing trend as sandstone, slate, SR sandstone, marble, and FR sandstone. The cluster growth of long needle-like ettringite crystal and strong preferential growth trend of Ca（OH）2 crystals would result in wider interfacial transition zone range of concretes made with fully rust-stained sandstone and marble aggregate, respectively. Therefore, the impurity aggregate content should be strictly controlled during aggregate selection.展开更多
As novel Zintl phases with the LiGaGe structure type,Ca1−xCexAg_(1−y)Sb has shown decent thermoelectric performance as well as complex structure transitions,which are closely related to the Ag defects in the anionic l...As novel Zintl phases with the LiGaGe structure type,Ca1−xCexAg_(1−y)Sb has shown decent thermoelectric performance as well as complex structure transitions,which are closely related to the Ag defects in the anionic layers.In this report,La/Sr co-doped materials,Ca_(1−x−δ)Sr_(δ)La_(x)Ag_(1−y)Sb(0≤δ≤0.7),were prepared and studied regarding relevant thermoelectric properties.Interestingly,the incorporation of alkaline-earth metal Sr suggested a different structure transition mechanism from the LiGaGe type to the ZrBeSi-type,which seemed closely related to the Sr doping concentrations.Besides,significant enhancement of the thermoelectric performance resulted.For materials with a specific composition of Ca_(0.55)Sr_(0.3)La_(0.15)Ag_(0.89)Sb,a maximum zT of 0.7 has been achieved at 823 K,which also corresponded to a high average zT value of 0.66 between 774 and 1068 K.展开更多
基金Under the auspices of the Taishan Scholars Project Special FundsNational Natural Science Fundation of China(No.42077434,42001199)Youth Innovation Technology Project of Higher School in Shandong Province(No.2019RWG016)。
文摘It is an important way to realize rural revitalization and sustainable development to guide rural settlement transition(RST)in an appropriate way.This paper uses actor network theory(ANT)to construct a theoretical framework for the study of RST.Taking two typical villages with different transition paths in rural areas of North China Plain as examples,this paper reveals the mechanism of RST and makes a comparative analysis.The results show that:1)after identifying problems and obligatory passage point,key actors recruit heterogeneous actors into the actor network by entrusting them with common interests,and realize RST under the system operation.2)Rural settlements under different transition paths have similarities in the problems to be solved,collective actions and policy factors,but there are differences in the transition process,mechanism and effect.The actor network and mechanism of RST through the path of new rural community construction are more complex and the transition effect is more thorough.In contrast,the degree of RST of retention development path is limited if there is no resource and location advantage.3)Based on the applicable conditions of different paths,this paper designs a logical framework of‘Situation-Structure-Behavior-Result’to scientifically guide the identification of RST paths under the background of rural revitalization.
基金The Strategic Priority Research of the CAS,No.XDA20040400National Natural Science Foundation of China,No.41871118,No.4202200。
文摘Energy development has a significant impact on urbanization. This study employs the entropy method to evaluate the level of urbanization in Central Asia and further analyzes the possible dynamic transition mechanisms of the impact of energy development (characterized by energy development scale, energy trade, energy consumption, and energy endowment) on urbanization using the Panel Smooth Transition Regression model (PSTR). The results demonstrate that energy development in this region is characterized by “three highs and one low”, namely, high production volume, high export volume, high endowment, and low self-consumption, and plays a crucial role in the progress of urbanization. A nonlinear relationship is found to exist between energy development and comprehensive urbanization in the transition economies of Central Asia. Generally speaking, as energy development continues to expand, its impact on urbanization in this region has shifted from constraint to promotion, with the latter gradually tending to flatten out. Energy development characterized by energy development scale, energy consumption, and energy trade can prove the point, whose threshold is 1.47 million tons oil equivalent (Mtoe), 0.29 tons oil equivalent (toe) per capita, and 20.95 Mtoe, respectively. However, not all energy development models exhibit this behavior. Energy development characterized by energy endowment is such a case where the positive effect of it on comprehensive urbanization will be restrained when it exceeds 3.18. These findings can aid decision makers in seeking a better energy development model to promote the sustainable development of urbanization in Central Asia, avoiding energy resources waste and disorderly development.
基金supported in part by National High Technical Research and Development Program of China(863 Program)under Grant No.2009AA01Z210National Key Basic Research Program of China(973 Program)under Grant No.2009CB320504+1 种基金Guangdong Ministry of Education Industry-Academia-Research project under Grant No.2009B090300315supported by the special program for joint construction project of Beijing
文摘IPv4 and IPv6 will coexist for many years during the transition period from the traditional IPv4-based Internet to an IPv6-based Internet.DHTLayer,a novel IPv4/IPv6 transition mechanism based on Distributed Hash Table(DHT) is presented in this paper.It can fully support IPv4 and IPv6 inter-operation.DHTLayer employs a DHT overlay to maintain the routing information between IPv4 and IPv6.It decouples path selection from packet delivery.In DHTLayer,the Looking-Up Route Path is responsible for selecting paths,and then the Delivering Process takes charge of delivering IP packets along the path selected above.Simulation results show that it is very effective and efficient.
基金supported by the National Natural Science Foundation of China (Grant No. 11172284)the International Science and Technology Cooperative Project from Ministry of Science and Technology (GrantNo. 2013DFA30820)
文摘This paper studied the active-to-passive oxidative mechanism of C/SiC composite under high temperature and oxidative conditions. An analytic model and computational method were established based on the process of gas diffusion in boundary layer and the equilibrium relations in surface chemical reactions. Simultaneously, an engineering equation to predict the oxygen partial pressure of active-to-passive transition was derived under the specific temperature zone. The results indicated that the active-to-passive oxidation transition of C/SiC is closely related to the composition of the material. At certain temperature and oxygen partial pressure conditions, the composite with high carbon content is prone to cause active oxidation which is negative to the oxidation resistance of the material.
基金financially supported by the National Key Research and Development Program of China (No.2022YFE03170002)the National Natural Science Foundation of China (Nos.52071286 and U2030208)。
文摘Efficient capture,safe storage and release of tritium from the international thermonuclear experimental reactor(ITER) reaction exhaust gas is a perplexing problem,and the development of an efficient tritium-getter material with ultra-low hydrogenation equilibrium pressure is considered as a reliable way.In this work,Zr_(2)Co alloy was selected as a tritium-getter material and prepared through induction levitation melting.Fundamental performance test results show that Zr_(2)Co exhibits an ultra-low hydrogenation equilibrium pressure of 3.22 × 10^(-6) Pa at 25℃ and excellent hydriding kinetics under a low hydrogen pressure of 0.005 MPa.Interestingly,unique phase transition behaviors were presented in Zr_(2)Co-H system.Specifically,Zr_(2)CoH_(5) formed by Zr_(2)Co hydrogenated at room temperature is initially decomposed into ZrH_(2) and ZrCoH_(3) at200 ℃.With the temperature increasing to 350 ℃,ZrCoH_(3)is dehydrogenated to ZrCo,and then ZrCo further reacts with ZrH_(2) at 650 ℃ to reform Zr_(2)Co and hydrogen.Among the staged phase transition pathways during dehydrogenation,the decomposition of Zr_(2)CoH_(5) occurs preferentially,which is well accordance with both the smallest reaction energy barrier and the maximum reaction spontaneity that are determined respectively from kinetics activation energy and thermodynamics Gibbs free energy.Furthermore,first principles calculation results indicate that the stronger binding of hydrogen in interstitial environments of ZrCoH_(3)and ZrH_(2) triggers the hydrogen-stabilized phase transformation of Zr_(2)CoH_(5).The unique phase transition mechanisms in Zr_(2)Co-H system can shed light on the further exploration and regulation of analogous staged phase transition of hydrogen storage materials.
基金Supported by the National Natural Science Foundation of China(Grant No.50373045)
文摘As an important kind of intelligent materials,shape-memory materials have been received increasing attention on account of their interesting properties and potential applications in recent years.Particularly,the rise of shape-memory polymers by far surpasses well-known metallic shape-memory alloys in their shape-memory properties.The advantages of polymers compared to other materials are their easier availability and their wide range of mechanical and physical properties.The polymers designed to exhibit a shape-memory effect require two components on the molecular level:crosslinks to determine the permanent shape and switching segments with Ttrans to fix the temporary shape.Up to now almost all papers on shape-memory polymers introduce switching segments with the covalent linking method.On the other hand,only several cases concern non-covalent interaction.However,the research works mentioned above is based on a single Trans(i.e.,Tm or Tg).
基金Supported by the National Natural Science Foundation of China under Grant No 11104331the National Basic Research Program of China under Grant No 2011CB921702
文摘Systemic measurements show that there is no 3D to 2D crossover in the reduction of the superconducting transition temperature Tc in Nb thin films. This result is consistent with all previous measurements while it is contrary to the prevailing understanding based on the interplay between proximity, localization, and lifetime broadening. Our study indicates that the decrease of Tc can be interpreted by the combined effects of electron-phonon coupling parameter λ and the defect scattering rate pw, being uniquely determined by their ratio λ/ρw. Other factors such as film thickness and irradiation do not produce additional effects beyond these two parameters.
文摘I am happy to attend this symposium at the invitation of the Tokyo Consortium. China and Japan are close neighbors, separated only bya narrow strip of sea. Exchanges have been frequent between the Chinese and Japanese peoples since ancient times. In striving for modernization,
文摘Effects of hydrogen on the mechanical properties of differently aged 7175 aluminum alloys were investigated by using cathodic H-permeation, slow strain rate tension and so on. The results indicate that both the yield stress and the percentage reduction of area decrease with increasing hydrogen charging time, and the degree of reduction decreases as aging time increases for the same hydrogen charging time.
基金financial support obtained from the Science and Engineering Research Board,Department of Science & Technology,Government of India(SB/S3/ME/0044/2013)Sponsored Research and Industrial Consultancy,Indian Institute of Technology Kharagpur,India(GAF)
文摘The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys （Al86Ni8Y6, Al86GNi6Y6Co2, Al86NigLa6 and Al86Ni8Y45La15） synthesized via mechanical alloying by varying the composition, i.e. fully or partially replacing rare earth （RE） and transition metal （TM） elements based on similar atomic radii and coordination number. X-ray diffraction and high resolution transmission electron microscopy study revealed that the amorphization process occurred through formation of various intermetallic phases and nanocrystalline FCC Al. Fully amorphous phase was obtained for the alloys not containing lanthanum, whereas the other alloys containing La showed partial amorphization with reappearance of intermetallic phases attributed to mechanical crystallization. Differential scanning calorimetry study confirmed better thermal stability with wider transformation temperature for the alloys without La.
基金the National Natural Science Foundation of China(12274170 and 52225203)。
文摘Lonsdaleite,also known as hexagonal diamond,is an allotrope of carbon with a hexagonal crystal structure,which was discovered in the nanostructure of the Canyon Diablo meteorite.Theoretical calculations have shown that this structure gives it exceptional physical properties that exceed those of cubic diamond,making it highly promising for groundbreaking applications in superhard cutting tools,wide-bandgap semiconductor devices,and materials for extreme environments.As a result,the controllable synthesis of hexagonal diamond has emerged as a cutting-edge research focus in materials science.This review briefly outlines the progress in this area,with a focus on the mechanisms governing its key synthesis conditions,its intrinsic physical properties,and its potential applications in various fields.
基金supported by financial support from the National Natural Science Foundation of China(Grant Nos.92164108 and U23A20322,51971188,51471139)the National Key Research and Development Program of China(2023YFF0719600)+4 种基金Hunan Provincial Natural Science Foundation(Grant Nos.2023JJ50009 and 2023JJ30599)the Guangdong Provincial Key Laboratory Program from the Department of Science and Technology of Guangdong Province(2021B1212040001)the Outstanding Youth Science Foundation of Hunan Province,China(Grant No.2021JJ20041)the Key Project of Scientific Research Fund of Hunan Provincial Education Department(Grant No.23A0150)the Chongqing Municipal Education Commission Science and Technology Research Program Youth Project(KJQN202101423).
文摘Doping is critical for inducing ferroelectricity in hafnia films,yet the underlying mechanisms remain debated.Here,through first-principles studies,we elucidate the pivotal role played by the complex phase transition mechanisms under carrier doping in understanding the origin of hafnia ferroelectricity.Specifically,electron doping orchestrates a metastable polar phase to stable antipolar phase transformation,driven by strong screening effects and weakened nonpolar covalent bonds,making n-type dopants rare.Conversely,weak screening effect and enhanced polar covalent bonding strengthen robust ferroelectricity,enabling significant ground-state phase transitions from the monoclinic to the polar orthorhombic phase and finally to the cubic phase under hole doping,a phenomenon prevalent in hafnia-based films doped with p-type dopants.Furthermore,this holeenhanced polar distortion also results in an inverse size effect in hafnia ferroelectric films,unlike perovskite ferroelectrics.Our findings offer new insights into the preparation of robust hafnia-based ferroelectric films through doping or interface engineering.
基金supported by the National Natural Science Foundation of China (No. 51331005)the National Science Fund for Distinguished Young Scholars (No. 51425402)
文摘Nb has a positive effect on improving the mechanical properties of metal materials, and it is expected to strengthen CoCrCuFeNi high-entropy alloys （HEAs） with outstanding ductility and relatively weak strength. In this paper, the alloying effects of Nb on the microstructural evolution and the mechanical properties of the （CoCrCuFeNi）100-xNbx HEA were investigated systematically. The result shows that Nb promotes the phase transition from FCC （face-centered cubic） to Laves phase, and the volume fractions of Laves phase increase from 0% to 58.2% as the Nb content increases, Compressive testing shows that the addition of Nb has a positive effect on improving the strength of CoCrCuFeNi HEA. The compressive yield strength of （CoCrCuFeNi）100-xNbx HEAs increases from 338 MPa to 1322 MPa and the fracture strain gradually reduces from 60.0% （no fracture） to 8.1% as the Nb content increases from 0 to 16 at.%. The volume fraction increase of hard Laves phase is the key factor for the strength increase, and the reduction of the VEC （valence electron concentration） value induced by the addition of Nb is beneficial for the increase of the Laves phase content in these alloys.
基金Funded by the Fundamental Research Funds for the Central Universities(WUT:142201001)
文摘The feasibility of using coral reef sand（CRS） in Portland cement concrete is investigated by testing the mechanical property and microstructure of concrete. The composition, structure and properties of the CRS are analyzed. Mechanical properties and microstructure of concrete with CRS are studied and compared to concrete with natural river sand. The relationship between the microstructure and performance of CRS concrete is established. The CRS has a porous surface with high water intake capacity, which contributes to the mechanical properties of concrete. The interfacial transition zone between the cement paste and CRS is densified compared to normal concrete with river sand. Hydration products form in the pore space of CRS and interlock with the matrix of cement paste, which increases the strength. The total porosity of concrete prepared with CRS is higher than that with natural sand. The main difference in pore size distribution is the fraction of fine pores in the range of 100 nm.
文摘This paper extends the flux scattering method to study the carrier transport property in nanoscale MOSFETs with special emphasis on the low-field mobility and the transport mechanism transition. A unified analytical expression for the low-field mobility is proposed, which covers the entire regime from drift-diffusion transport to quasi-ballistic transport in 1-D, 2-D and 3-D MOSFETs. Two key parameters, namely the long-channel low-field mobility （λ0） and the low-field mean free path （λ0）, are obtained from the experimental data, and the transport mechanism transition in MOSFETs is further discussed both experimentally and theoretically. Our work shows that λ0 is available to characterize the inherent transition of the carrier transport mechanism rather than the low-field mobility. The mobility reduces in the MOSFET with the shrinking of the channel length; however, λ0 is nearly a constant, and λ0 can be used as the ＂entry criterion＂ to determine whether the device begins to operate under quasi-ballistic transport to some extent.
文摘The cuticle of a maggot goes through a mechanical transition when it dries, increasing in stiffness by about an order of magnitude (e.g. from 0.5 GPa to 5 GPa) as the water content drops from about 1 g/g (weight of water per unit dry weight) to 0.4 g/g. Thus stiffness represents the loss of freezable water and is more or less diagnostic of a material stabilized by hydrogen bonds. Further loss in water results in a smaller increase in stiffness. In natural systems the water content is controlled by the addition of phenolic residues, resulting in tanning or sclerotisation, which drives the matrix components towards co-operative interaction and makes the material permanently waterproof.
文摘Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of rubidium metal hydrides RbMH4（M = B, Al, Ga） for five different crystal structures, namely hexagonal（P63mc）, tetragonal（P42/nmc）, tetragonal（P421c）, orthorhombic（Pnma） and monoclinic（P21/c）. Among the considered structures, tetragonal（P421c） phase is found to be the most stable one for these metal hydrides at normal pressure. A pressure-induced structural phase transition from tetragonal（P421c） to monoclinic（P21/c） phase is observed in all the three metal hydrides. The electronic structure reveals that these hydrides are wide band gap semiconductors. The calculated elastic constants indicate that these alkali metal tetrahydrides are mechanically stable at normal pressure.
基金Funded partly by the Major State Basic Research Development Program("973"Program,Nos.2015CB655101 and 2013CB035901)the National Natural Science Foundation of China(Nos.51379163 and 51579195)
文摘We investigated mechanical properties of concretes made with impurity aggregates of different combinations. Besides the mechanisms were explored by EDS, CT, and hardness testing. The results showed that fully rust-stained and surface rust-stained sandstone aggregate had significant adverse impact on the compressive strength of concrete while sandstone aggregate had a much more obvious impact on the ultimate tension of concrete. Concrete crack was more prone to expand along surfaces and the micro-hardness of interfacial transition zone of different aggregates was ranked in decreasing trend as sandstone, slate, SR sandstone, marble, and FR sandstone. The cluster growth of long needle-like ettringite crystal and strong preferential growth trend of Ca（OH）2 crystals would result in wider interfacial transition zone range of concretes made with fully rust-stained sandstone and marble aggregate, respectively. Therefore, the impurity aggregate content should be strictly controlled during aggregate selection.
基金financial support from the National Natural Science Foundation of China(Grant No.51771105 and 51271098).
文摘As novel Zintl phases with the LiGaGe structure type,Ca1−xCexAg_(1−y)Sb has shown decent thermoelectric performance as well as complex structure transitions,which are closely related to the Ag defects in the anionic layers.In this report,La/Sr co-doped materials,Ca_(1−x−δ)Sr_(δ)La_(x)Ag_(1−y)Sb(0≤δ≤0.7),were prepared and studied regarding relevant thermoelectric properties.Interestingly,the incorporation of alkaline-earth metal Sr suggested a different structure transition mechanism from the LiGaGe type to the ZrBeSi-type,which seemed closely related to the Sr doping concentrations.Besides,significant enhancement of the thermoelectric performance resulted.For materials with a specific composition of Ca_(0.55)Sr_(0.3)La_(0.15)Ag_(0.89)Sb,a maximum zT of 0.7 has been achieved at 823 K,which also corresponded to a high average zT value of 0.66 between 774 and 1068 K.
